Experiments in motorising a Float Tube.

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Fitting an Electric Outboard to a Float Tube.

Part 1. (This set of notes will need splitting to replies in order to fit the text length limitations of this website).

Over the last fifteen months, I have seriously started a project to motorise a float tube. This is definitely not a project intended to stick a two stroke/petrol outboard unit on the float tube, as it is too heavy to carry to the water. Additionally, the management of the drinking water authority reservoirs we fish over, would generally definitely not like the oily exhaust! Electric power is therefore the most feasible answer.

The need for this modification:

The intention of this device, apart from satisfying my curiosity, is simply as an assist device to travel back against the wind if you are weak or incapacitated – or even I suppose if one is lazy. This problem with strong winds as I well know from bitter experience, can be quite debilitating  when you are a long way from the landing station and are somewhat beyond your prime. Hence recently in the BFTA some of us older chaps with dodgy knees, arthritis and troublesome hearts, are now getting new float tubes with oars attached. In reality this project is not intended as a lazy way of tooling around a water, nor eliminating the hassle of putting fins on. Neither is it intended as a way of taking up trolling for big-uns! The battery size and weight of the equipment will be the limitation for weaklings. Under normal conditions the fins will be the usual form of driving power, with the motor saved for reserve help or emergencies.

The following is a set of notes giving the benefit of any experience which I have gleaned over the course of my experimentation. Hopefully, it will help anybody else with an interest in a DIY drive system for their float tube. As far as I am aware, nobody else has attempted this in the UK, and if they have they have kept very quiet about their work. This has therefore necessitated that I ‘start from scratch’. Internet searches yield surprisingly sparse information, and that which I have seen, has generally been quite crudely constructed, or at times incorporate what I can only consider downright dangerous practice. Both the USA and Europe have examples of attempts demonstrating varying degrees of competence. I do have quite a wide experience of ‘design’ and making things to draw on and to be fair there is a reasonable amount of useful kit in my workshops if I need it.

Over the course of my experiments I have discovered that a float tube appears to have a far higher drag factor than I would have suspected. From my experience, a motor which will apparently easily move a fibreglass boat tender, or a polymer kayak, finds it much harder going when moving a float tube such as a Guideline Drifter, or alternatively a Snowbee Prestige. (These have been the ‘mules’ for my experimentation).  I guess dangling feet and fins plus a loaded fish bass have a deleterious additional effect on drag. In a wind, a high riding tube also has a sizeable ‘sail’ drag effect factor as well.

Batteries for powering the motor:

This is the area where a lot of thought needs to be put into the project. ‘Normal’ lead acid batteries tend to be very heavy. Additionally, you wouldn’t really want a load of sulphuric acid tipping over you - or the float tube case either! They also need to be what are classed as ‘leisure batteries’ because of the deep cycle characteristics. An ordinary car battery is not designed to produce steady power for any length of time.

At this point sealed AGM / Gel batteries come to the fore because they can be used upside down or on their side etc. without any danger of spilling. They also come in a wide range of sizes and amp/hour ratings. Some are specifically designed for marine use and others for powering mobility scooters – these are ideal because they are deep-draw batteries designed to power motors over a relatively long period. They are however quite weighty for their relatively compact size - a 22ah AGM battery will weigh around 7kgs.

As an aside, I have been astonished to discover that AGM batteries will carry on working when totally submersed in water – I would not suggest trying this in salt water however! (This revelation has come as the result of accidental soakings when various battery box seals failed to do their job).

At this point we need to sit back and think very carefully. Lithium batteries are also available. They have a greatly reduced weight, (one third to half the weight per amp/hour), and a much better performance curve than lead acid AGM batteries – nearer to 90% as opposed to 60% for a good AGM battery. HOWEVER, LITHIUM AND WATER VERY DEFINITELY DON’T MIX! An explosion or fire could occur if they do come together. All is not lost though! Lithium Ion, and I would suggest Lithium Polymer (LiPo) batteries, in my humble opinion should be avoided! There is a third type, now fairly commonly used for driving Golf Trolleys, which is designated LiFeO4 – this is a pretty stable variant and less likely to explode. It doesn’t have quite the performance of the other two but is very much safer. The other downside is the cost, which amounts to between three and six times as much per amp/hour. If you do go down the Lithium battery route, then make sure you design a very waterproof box or bag to keep it in, and also keep it up out of the water. (Cold water reduces the effectiveness of any battery anyway).

I am aware that there are other chemical composition / mixed lithium batteries as well – but my current humble advice is stick to LiFeO4 if you wish to avoid an opportunity to participate in the fabled ‘Viking Funeral’!

Surprisingly few golf trolleys have waterproof containers for these batteries, so the conclusion must be that they are at least tolerant of a little water contact – (or alternatively all golfers using them are fair weather types)!

If choosing a LiFeO4 lithium battery from a golf trolley, they are usually sold with a specific charger for the battery, (don’t plug your expensive new lithium battery into a normal lead acid battery charger, otherwise you will probably destroy it). These units also appear to come in two case types – one with a charger port on the side, and the other with just two terminal connections on the end of the case. The battery type with the charger port on the side has the disadvantage of being a potential ingress point for water if the battery accidentally gets wet. The better proposition is the type with just the end terminals. Both types may have a Torberry T bar connector hiding the terminals, these are usually fitted with two screws and can often be removed to expose the normal terminals to make wiring to the motor easier. Otherwise, you can use the T bar and buy some Torberry Anderson connectors from ebay and make your own adaptor.

LiFeO4 Golf trolley batteries come mainly in two types – 18 to 27 hole variants which are usually 16ah batteries (cost about £130), and 27 to 36 hole versions which are classed as 20ah. (cost around £155 to £220). A 20ah lithium based battery will allegedly work similarly to a 24ah AGM cell, this is because of its flatter discharge rate with less drain deterioration under load.

You can work out how big you want your battery by doing the amp hour motor usage drain, divided into the size of the battery you are thinking of using. i.e. a battery rated at 21ah powering a motor drawing 10ah would theoretically supply power for around two hours. In practice you would probably get a bit less than this.

Which motor:

Obviously a balance between thrust power and the amps drain required to achieve it, are the paramount concerns here. However, having said that your motor needs enough power to drive the float tube, and you, plus gear, also a full bag of heavy fish through the water against the wind. I had to make a choice and see whether it worked. So here is the benefit of my experience.

I reckoned a motor somewhere between 18 and 30lbs thrust was required. At its lowest speed setting an 18lbs thrust motor should draw between 7 and 9 amps rising to around 15 under top speed heavy load conditions. You would be lucky to get a 28 or 30lbs thrust motor to draw much less than 27 to 32 amps. The trade-off is time running against power needed. In theory a motor running at 15 amps would run for an hour on a 15ah battery – in practice you would probably not get this long because of a number of contributory factors.

There are a number of motors available within this range, although they tend to be a lot more expensive to buy at around the 28 to 30lbs thrust  level, than their larger 40lbs plus stablemates. Minn Kota have a couple in their range, Bison and a number of Chinese derivatives can also be bought. However, Jarvis Marine of Australia, make a couple of very light small motors - the ASP18 and the ASP24 which cost between about £71 to £135 depending where you source them from. Kayakers have caught on to these in the last year or so and their price has increased over that time. I have both variants of these latter motors; both have pro’s and con’s. Watersnake is the brand name. There are at least two other bigger thrust variants suitable for FT’s in the Watersnake range – but they do draw a lot more electrical power and cost quite a bit more.

From experience the Watersnake ASP18 will drive a float tube quite well in calm conditions. Backing up against a strongish wind would require the higher speed rating and necessitate ‘tacking’ to make any headway. The ASP24 is definitely a stronger motor and better for the job against the wind, but it does use more power and create a higher battery drain. More power equals less running time or a much heavier battery!

Having decided on an electric motor to buy, the major decisions then start to appear; should it be a powerful unit, or one which will assist gently? How many amps will it draw from a battery, and therefore how big a battery will be required? Where will the battery go on / in / around the float tube. Where to fix the motor, on what, and again how? Etc. etc.

Making the frame to hold the motor on the FT:

The most common material for making support frames, which is readily available and easy to work with, is UPVC drainpipe. This material has a useful selection of fittings such as elbows, tees, end stops etc. It can be cut with a hacksaw and joined with UPVC solvent glue. Be aware that not all makes of pipe will be joined by this glue unless you get them from the same manufacturer source. Carefully work out the order in which to assemble the pieces, and make sure you get the angles correct first time as there is very little chance of moving the joints once they go together. By judicious use of a good hair dryer, oven, or blown air paint stripper, you can heat the pipe enough to flatten it if needed. Making bends by heating the pipe is not really possible unless you can devise a flexible internal support system. You only really need a hacksaw, tape measure, file and a Stanley knife to work with this material.

The next other easily worked material is wood. Exterior WBP or marine grade plywood is favourite for cutting out shapes to go around curves. Any joints will need to be made with waterproof resin glues, and perhaps screws as a second line of defence in case a joint separates. A couple of good coats of yacht varnish should keep the water out when the frame is finished. Ideally, one could laminate frames up from strips of constructional veneer cramped around home-made formers – this would produce neat slim-line frames. It is however a lot of work to do this. Steam bending could also be used to produce the shapes – but again formers would need to be made. Wood is my least favourite choice for making the frame – it is a lot of work, time consuming and potentially bulky.

From experience I discovered that by far the strongest and easiest material to use is 15mm copper pipe. A vast selection of joints and fittings are available for this material. To work with copper you will need a pipe cutter, possibly a fine tooth hacksaw, a medium or fine cut file, a gas blowtorch, a 15mm pipe spring and maybe a 15mm pipe bender. Fine abrasive or steel wool to clean the joints, solder and resin flux complete the requirements - apart from any fittings needed.

15mm pipe fittings come in two types as far as being useful for this task is concerned – the first is pre-solder ring, where the solder is already contained in a raised ring around the joint. This type is easy to use, but a little more expensive than the more basic fittings, which are totally plain without any solder. This latter type makes a neater bump-free joint but it  does need a little more skill to make the joints. Don’t be put off by the need to solder, it is an easy skill to learn if a couple of basic rules are followed. ALL mating surfaces, (including the inside of the fittings), should be cleaned with fine abrasive, steel wool or abrasive nylon ‘scrubbing pads’ – then DO NOT put your fingers on the newly cleaned surfaces. Each surface should then be fluxed with the resin based flux, which will prevent oxidation of the surface and promote solder flow when making the joint with a blowtorch. After assembling the parts, heat over the whole area of the fitting and pipes then bring the flame just off the end of the joint, when hot enough the solder will run out of the solder ring by capilliary action towards the heat. (You will see a silver ring appear at the end of the joint). Leave to cool naturally rather than chuck water over it. With the plain fitting, the same heating method applies, but this time just before applying the solder to the end of the fitting when estimated as being hot enough, move the torch down to the middle and it will ‘suck’ the solder into the joint as soon as it melts on the end.

Cutting lengths of pipe is easily achieved with a small pipe cutter, which rotates around the pipe and gradually tightens a cutting wheel against it. The cheaper type requires you to tighten a screwed handle after every rotation, or a slightly more expensive version clamps around the pipe and tightens itself as you rotate it. Both will do the job equally well. A 15mm pipe spring can be inexpensively obtained from Toolstation or Screwfix, or a little more expensively at DIY outlets. You will feed this spring into the end of the pipe to support the inside and prevent crushing when you make bends. (You will probably first have to get a strong screwdriver to feed up the end of the tube, rubbing it around the inside of the cut, to remove the pipe cutter burr by ‘burnishing’ the inside of the cut). Pipes can be bent around your knee a bit at a time, or wrapped round a strong tin or tree trunk. The copper tube is thin, usually annealed and easy to move; just do it steadily! If you wish to make tighter bends without resorting to right angled or obtuse soldered joints, then a pipe bender will be required. The cheapest supplier of pipe, elbow fittings etc. that I have found is Toolstation. (I have no particular allegiance or employment to this company). Ebay searches can also yield some bargains.

Keeping webbing in place can be achieved by bending up shallow “U” shaped lengths of copper wire core, scavenged from heavy duty mains electrical cable. Drill suitable sized small holes in the appropriate place on the copper frame tube, and then solder them in position.

Specifically designed and now commonly available electric outboard boat motors appear to be the simple answer to the propulsion dilemma. However, most need a substantial deep drain leisure battery of considerable amp hours to drive them along. I do have a couple of 120ah examples of these batteries in my motorhome, but would risk breaking my back to get one out, and it would certainly set a float tube a bit low in the water! Not a sensible solution then!

A while back I came across an advert for a Jarvis Walker ‘Watersnake’ electric outboard. They do four variations, but the smallest one is rated at 18 lbs thrust. (ASP18) The next one up is a 24hp version (ASP24) of identical dimensions, but which has the advantage of a tilting transom mount. The main shaft is around 24” long. Upon further investigation, I discovered that the smaller motor only draws about 7 to 9ah at the lower of the two speeds, and about 15ah at the higher speed. To a simpleton, this indicates that a 21ah Gel Battery could provide up to a couple of hours use at the lower speed, allowing for batteries not performing too well when the voltage starts to drop etc. 22ah AGM batteries are readily available for golf caddy trolleys and mobility scooters. Indeed, if you are registered disabled, you could even get your mobility scooter battery VAT free, take it off the scooter and use it on your float tube. These batteries are designed for deep drain heavy use, BUT MUST BE RECHARGED IMMEDIATELY AFTER USE. They also lose around 3% a month when left standing, and don’t respond well to being left flat. However, they weigh about 6.5kgs to 7kgs. That’s a bag of fair fish isn’t it?

First steps:

To cut a long story short, the wife asked me what I wanted for my birthday, so after due consideration I asked for the smaller Watersnake motor. At the time it was not much cheaper than the 24hp version, but it does draw considerably less amp hours from the battery. Both of versions of the motor only weigh about five or six lbs, so are not heavy to hang wherever you decide to put them. They are also advertised for pushing a kayak along. There are also reports of fibreglass small boat tenders being powered by them, so in theory they should be up to the job. There are some Youtube videos on the net of USA and European fishermen using them in calm waters.

When the motor duly arrived it is proved to be very neat little toy. It is very definitely not built like a tank, but with careful use it should do the job. The 24” motor shaft lifts up through the transom bracket and is secured in place by a little plastic ring collar and also a clamp bolt, so that it can clear the bottom of the lake when landing or launching. (I can see this being replaced with a brass or aluminium version when I get time to turn one up).

To mount the motor, Messrs. Toolstation have received a considerable amount of pension in return for a sack full of 32mm various pipe fittings and a length of UPVC pipe. Ebay companies have supplied me with lengths of 40mm webbing and lots of buckles and bits. This is not a seriously cheap experiment is my latest conclusion!

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Part 2.

Now the serious question of how, and where, to mount the transom.

There are four main choices, these are:-  

Position 1.   On the pointy bit at the front – but this is behind your seat, difficult to reach, (possibly impossible if you have a crippled back). Additionally, from experience, the tiller arm will need extending / cranking). You may also need to make a remote switch box to control the motor because it is very difficult to turn and reach so far back in most FT’s. The motor head also needs turning 180 degrees so the controls face you from behind. Some of the Youtube videos show Americans sitting across the tubes with their feet out of the side to enable them to reach the controls – (in my company they wouldn’t)!!!

Position 2.   On the ends of the sponsons in front of you. This has the advantage of pushing on the centre line of the float tube. You can also see what it is doing, and get at all the motor controls. The disadvantages are that the shaft and motor are in the way of your feet when finning, and there is a high likelihood of getting a sinking line wrapped up in a prop. A lively trout or a double hook-up would have a marvellous snag to get itself tangled around. I would suggest devising a prop guard, or ring shield around it, to try and protect fins and waders if developing this idea.

Position 3.   On the side of the float tube. There are disadvantages in that the power force is not on the centre line, but any yaw could theoretically be countered by turning the motor to correct it. It will need mounting so that the prop doesn’t turn into the sponson, or foul your waders when on an angled course. There are a lot more advantages:- the motor can be mounted beside you so it is easily to hand. It will be easy to lift or lower for launch or landing. The control switches are right next to you. It should be easy to disconnect or connect a battery if you carry two and have fitted a waterproof socket in line with the motor. If you can’t be bothered to lift the motor, a simple hinged transom plate could be easily made and operated next to you.

Position 4.  Between your legs tight against your crotch, so as to be as much out of the way of your feet as possible, and as close to the seat as you can get. This position will be tricky to achieve for easy access and egress from the FT, and I suspect very uncomfortable on ‘bouncy waves’.

Position 5. Under the seat.

The first Design:

I decided to try a side mounted arrangement as in 3 above.

I duly got onto the bandsaw and hacksaw and chopped a lot of bits of pipe up to make a side mount frame, on which I screwed a piece of 20mm exterior grade WBP plywood for a transom. 32mm PVC pipe appears to be the universal float tubing accessory construction material, favoured by those in the USA who have had a DIY go at solving this problem, and also that of rod holders etc. Although I would personally prefer to bend a frame up in aluminium given access to the pipe bending formers etc. (I have a tame TIG welder who could be called on if required). As a further idea 15mm copper pipe is not very heavy and is easily shaped and soldered together. (See a later design).

PVC solvent grabs and sets instantly I discovered!

I now cobbled together various webbing attachments and buckles etc. to fit this new frame to D rings on the float tube. The result was impressively neat and solidly mounted. The motor was indeed easy to access and operate. It did drive the float tube! Except it didn’t easily go where I wanted it to. When in the wind, the idea of turning the motor slightly to the side to counteract yaw, proved a total fallacy – in fact the tube probably moved better when the motor was turned 180 degrees so effectively it was pushed sideways!? You live and learn, so it was back to square one!

Conclusion and my advice equals – Don’t waste your time on this method!

For curiosity while tooling around on Toft, I released the motor from the transom mount on the side and loosely placed the bracket over the crossbar between my legs. Taking care to keep fins and waders to the side, I switched on and held on tight to the motor head – the response was enough to tell me that the motor would move the FT in a straight line when it was placed on the centre line of the FT. I guess this was obvious, but it did reinforce and confirm the point. The tube could be steered both with fins, and also by a remarkably slight turn of the motor head, which was interesting to mentally note and encouraging for further development.

A Mark Two:

A second frame and transom was now constructed from UPVC, but this time it was fitted to the pointed bow end of the Snowbee Prestige. (As in position one listed above). The Snowbee has some very useful D rings affixed to the case near the bow, which made very convenient mounting points for the webbing straps. The frame itself was also trapped to some extent by the inflation of the tube. However, the two UPVC tube frame halves needed to join in quite a narrow line down the inside of the bow crease/joint. This required cutting most of the lower lugs off the two adjoining elbows and trying to glue them together. The Floplast UPVC adhesive wasn’t up to the job and an epoxy mix was finally used – (this later proved inadequate as well). If building the frame again I would not use UPVC but 15mm copper tube instead.

The motor head on the Watersnake was now turned 180 degrees so that the switches and tiller handle pointed forwards towards the back of the FT seat. In essence this was a simple remove one bolt and rotate the head round the downshaft – but nothing is ever simple is it? It also required taking the lid off and carefully repositioning the three wires which go down the tube to the motor. AT this point it was discovered that the wires pass through quite roughly cut slots at the top of the downtube which cut into the insulation around the relatively short wires. Insulation tape was duly required and applied to avoid a short circuit. (This was also true on the ASP24 as well). Some may wonder why bother turning the head, because the motor has two forward and two reverse speeds. The reason is that in theory the prop doesn’t work as effectively in reverse.

On the water, this system works very well once it is switched on. The tube can be fixed to travel in a straight line by tightening the plastic clamp bolt on the motor down tube. Steering of sorts can be obtained by use of the fins. If you are able to reach behind to the tiller, quite sharp turns can be made. Operating the motor switches is just about achievable, but seriously difficult if you have back problems or limited shoulder movement.

The tiller can be extended, and there are commercial telescopic handles available – but be warned they have a 40mm clamping hole and the motor tiller is only about 25mm, so you will have to have the wherewithal to turn up a sleeve adaptor if you wish to use one. I was caught by an advert claiming these handles fitted the ASP18 & 24 Watersnakes – THEY DON’T! I did make a nylon sleeve, but found even the extended tiller on the centre line is quite hard to use.

I have since fabricated a cranked handle from aluminium tube – this 25mm tube was manufactured as a cranked TV aerial mast and sold by Toolstation for a lot less than a fiver. The addition of a 1” rubber handle grip and a sleeve end turned out of a short length of 32mm aluminium pipe, obtained on Ebay, completes a lightweight workmanlike extension. (A metal turning lathe is handy here)! A nylon ring turned, and epoxy glued, over the end of the sleeve makes fitting a clamp bolt an easy fix.

Remote electrical control of the motor:

Quite early in this design I decided to extend the switches to a switch box which could be moved forward and placed by the angler’s side. Initially I made a box which had new switches and doubled up to the connections on the back of those in the motor head. In reality you only need five 20amp capable wires to come forward, as the other four connections can be made as links in the back of the new switchbox. The wiring diagram can be found and downloaded from the Jarvis Walker site on the internet. Initially I brought the wires out of the bottom of the motor case through a 13mm hole into a six pin plug. An idea which makes it easy to return the motor to native mode if you do not wish to permanently use the remote control box. The idea was eventually temporarily abandoned due to the difficulty in finding a neat, sufficiently electrically strong plug and socket capable of carrying the full load current draw, and which lead to poor reliability in use. (I have had some different new plugs on order for about two months now).

A second attempt at making a remote switch box entailed removing the two switches from the motor head unit, then fitting them into a project box obtained on the Internet. This box also incorporates a digital voltmeter to keep a rudimentary check on the voltage in the battery. You can also check the effect of running the motor at either low or high speed. (Fitting an Ammeter capable of reading at least 20 amps would also be a useful addition). The wires are directly coupled to the appropriate originals using spade ends which connect into the works fitted 6.2mm terminals. (This doesn’t damage anything in the original motor in case a warranty claim is required). In turn, the new connections are taped over with insulation tape to ensure they do not separate in use.

Anybody wishing a simpler remote control solution could set the switches to the desired speed and direction on the motor, then ‘break’ into the live wire with a simple on/off switch mounted in your remote box. This would only require two wires, one going forward to the switch and a return from the switch. This does limit the flexibility of the motor controls however.

Battery boxes:

Without doubt this has been the most difficult aspect of the whole project. Making a waterproof box to house the battery has proved extremely problematic. An initial bright idea was to use a good quality sealed ‘click-lid’ food box and make sure the lead came out through a hole with carefully and generously applied silicone mastic to keep the water out. In practice these boxes may be airtight in the kitchen, but they would make superb aquariums when used in the water. I know not how, but they completely fill up and drown the battery in use – particularly if placed on the floor behind the FT seat.

Masterplug sell a box claimed to be weather and waterproof, to keep mains extension leads and other electrical items dry. All I can say is that the one I bought is a total failure. I have modified the seal and applied quite a lot of mastic to areas which look suspect. I also screwed down the outlet cable bar to make a stronger seal, so maybe it will improve in use. (I hope so because the intention is to place a lithium battery in it).

Decathlon sell a range of waterproof kit bags for kayakers and hikers.  The 10 litre offering was bought and tried out. It is a bit tight for anything other than a 7ah battery. It certainly isn’t watertight if sat on the net floor behind the FT seat. However, on another occasion when the weather wasn’t quite as wild, and the bag was hung from the motor frame with the power lead firmly held facing downwards, it did serve the purpose and very little water got in. I have considered fitting a waterproof electrical gland through the side of this bag – that’s one which clamps a rubber seal onto a cable. With a couple of rubber washers and lots of silicon mastic it should be quite waterproof if the ends of the cable are sealed.

A more successful system was to use a large electrical junction box. This has two terminals, (brass nuts and bolts), fitted and threaded through the side, again with silicone mastic, but this time with the addition of rubber washers either side of the box wall. The battery is connected inside the box and a separate plug connection screwed on the outside for the motor plug. In addition to the rubber seal under the lip of the lid the joint is taped round with insulation tape. This has kept water and battery apart, but the problem now is how to fix the box above the water level without drilling any more holes in the case. Band straps are one answer. The battery is totally isolated in the box, but can be charged through the terminals on the side – not ideal because they should be charged in a ventilated area. I built two of these boxes, one for a 7ah AGM battery and one for a 22ah AGM battery.

A 7ah battery will drive an ASP18 for a surprising amount of time I discovered. I have run for around 35 minutes intermittently on low speed and guess it would have gone more time. This was originally intended as an emergency back-up if the main battery died.

Conclusion – Try to mount the battery in a watertight box mounted on a frame well above the waterline. Ideally, position it under some sort of drip cover / pagoda to stop rain and breaking waves directly hitting it.

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Part 3.


An alternative answer to positioning the motor:

For an early experiment, I have an old, but damaged, simple electric outboard, which I used about 40 years ago on a Tabur Yak II, this would push it along the Thames and even in light seas. I cannibalised the motor unit by removing it from the broken downtube, then fixing it to a frame clipped to the D rings under the FT seat. This has the advantage of putting the motor drive central on the float tube, thus largely out of the way of kicking legs and errant sinking lines. (This latter problem will always be there - how often have you drifted in the wind to find your line has wrapped itself around your legs and fins)? The major disadvantage is that it is under the tube for launching and landing, and on rocky shores is particularly prone to damage. An answer to this problem is to build a pair of ‘sledge’ runners into the frame either side of the motor. If you can get hold of an electric outboard with a suitable thrust range this is the easiest answer to the propulsion system. On my adaption, the thrust power is insufficient to move the tube very quickly. I have yet to try a better prop on the motor to see if it can be improved. This does illustrate the difference in drag moving a float tube to that of a polymer dinghy. Control is by a simple on/off switch in a remote box by the seat – this gives a forward only, or off, option. Steering is by moving feet and fins.

I suspect that some of the motors which are used on modern RC racing cars would also push a float tube along – some of the types my oldest son used when in the USA were incredibly powerful. They would however need considerable gearing down to avoid ‘overload burnout’, and or cavitation, on the prop. Mounting them in an aluminium tube with a good lip seal has no end of possibilities. I guess for the computer savvy, digital technologists, with facilities for printing plastic 3D shapes, this is an even more interesting possibility.

Marijn de Jong, of the Dutch based company Float tubes UK, has available a recently produced clever commercial design, which sits the motor and Lithium batteries in a waterproof housing fitted under the FT seat. However, this admittedly nice looking piece of kit will set you back well the wrong side of £1300. There is also an American company which has an earlier but similar system. The latter unit appears to be controlled by a wireless rheostat and switch box for motor speed, and on / off. Steering appears to be achieved by use of your fins.

I have some knowledge of a few gentlemen coming up with motor drive solutions constructed from battery powered electric drills. Indeed, there are a few examples on Youtube, including one of the crudest wooden constructions which emulates an outboard. This is ‘manufactured’ with a right angled screw driver head to fix the propeller to. Yes, these things will move a float tube, but I reckon you would need quite a few recharged batteries to get out of the Markfield arm back to the lodge against the wind at Thornton. If I were to develop and go further along this route, I would produce a straight line tube with a lip-sealed bearing at the lower end where the prop fits, and manufacture some sort of crossbar clamp/hook to clip on the float tube when the device is required – this would resemble the type of outboard drives the Amazonian Indians use on their dugout canoes, (but obviously on a smaller scale - and facing out of the front rather than the back of the watercraft). I would also solder a couple of wires into the drill case/switch and bring them out to a sealed Gel cell battery of suitable amperage so as to provide a few more stored ergs. The drill case would require waterproofing without compromising air cooling as well!

Some years ago a company in the USA produced a mini float tube which could be strapped to the front or back of the FT. This little FT carried the outboard motor on a centre mounted transom and the downshaft went through the floor, (where an anglers feet go on a full sized variant). The rest of the space was taken up with a lead acid leisure battery similar to a small car battery. It worked, but the company has apparently gone out of business. I guess controlling the motor switches and tiller as noted above was one problem. The retail price might well have been another. Getting it to and from the water was also an aggravation factor I suspect.

The Watersnake ASP18 & ASP24 transom mount:

The transom mount on the ASP24 is a tilting unit. Press a red button on the mount and it can be tilted to several different angles up to 75 degrees or so. This is not easy to do on a bow mounted motor. However, if you decide to try and mount a motor on the front of the float tube near the crossbar then this unit has distinct advantages. When launching or landing, the obvious one is that the motor can be tipped up to ride just under the surface, rather than let it crash about in the mud where the propeller could get damaged. On an ASP18 you could slacken the clamp bolt and lift the unit vertically in the mount, – BUT the propeller is still quite close to your legs and could get in the way of finning. With the motor tilted, there is far greater clearance for your legs.

It is possible to buy a transom mount on its own as a spare unit. It is not cheap at nearly £40. (Devon Angling on Ebay). If you get one then all you have to do is disconnect the wiring on the switches in the lid of the motorhead case, remove the clamp bolt, then lift the whole case off the down tube. Next remove the plastic clamp off the tube, then slip the original transom mount up and off.  At this point it would be worth checking the motor wires where they fit into the slots on top of the down tube – insulation tape them to reinforce and insulate any cuts. (Both my motors had this fault). The replacement tilting transom mount can now be slipped on. This is followed by a replacement plastic clamp. The head can now be bolted back across the tube and the switch wires reconnected. (You will of course have taken careful note of where they go before taking them off)!

This tilting transom mount is not an absolutely necessary modification to the ASP18, but it is a better mount and gives more versatility. The original plastic mount on the ASP18 will bend when tightened against the transom – if not tight it will slip. (I drilled two shallow holes on my plywood transom plate to let the clamp plate washers down into the surface thus preventing slippage. The drill bit for mounting kitchen cupboard door hinges is ideal for this). This latter modification is also good for firmly fixing the ASP24 - which does need more clamp power.

While mentioning the plywood transom plate, the best fixings to hold this to 15mm copper tube, are munson rings and bases. On the ASP18 I did use copper pipe strap type clips, this worked OK. However, the extra thrust of the ASP24 stretched and distorted these, so the munson rings were obtained and to date appear to work well. (Don’t drill the copper pipe and screw the transom plate direct, because the holes will let water into the frame).

The cost!

As stated above early on in these notes, achieving a motorising system is not cheap. If you are rich - go and get a ready-made system from Holland, (it looks a cracking good system). If you want to do it for £50 – then good luck and get real! If using AGM batteries and a Watersnake, you could achieve a serviceable unit for £150 to £200 including the copper tube mounting frame.

Final Conclusion:

If starting from fresh now, I would purchase a Watersnake ASP24. This would be powered by a LiFeO4 lithium 36 hole, end terminal golf buggy battery. The battery would be held in a sealed box above the water level and this would preferably be sheltered itself. The frame would be purpose designed from 15mm copper tube, and individually fitted to the particular float tube it is to be used on. (This is problem common to any float tube - the frame will have to be specifically individually designed). The frame will fit over the curves of the sponsons, so as to have some degree of being trapped on to it and held in position. The frame will be tightly hooked to at least four fixing points, (usually D rings on top of the sponsons and under the seat), by nylon webbing straps 40 to 50mm wide. Nylon hooks, snap buckles and adjustable strap clamps will enable a quick fix or release to the fixing points.

A remote switch box and cranked long tiller handle are needed for a bow mounted motor to be relatively easy to operate.

This is basically my current system. It is mounted on the bow of the float tube. What I haven’t stated with certainty is where is the best place to mount the motor? I am currently designing and building a front mount to try out. I know that another BFTA member is also looking into this configuration. I appreciate that there are problems, some of which are stated above, but the acquisition of the tilting transom mount may help overcome some of these.

If you wish to motorise a float tube I hope this little set of notes has been of some use to you. Do use 15mm copper tube for the frame - it is strong light and durable. The motor choice is down to you. In practice the ASP18 is a little light when used in a strong wind, but brilliant in calmer conditions. If you are disabled or elderly, then motorising a float tube is definitely a means of keeping you fishing for a while longer. I have proved the system does work, although I am still in the process of making refinements to make life easier for the failings of my body.

I wish you luck and tight lines!

[bracken]

Part 4

Fitting a motor in Position 2 on the sponsons in front of you.

As noted above this position has distinct advantages and some very pronounced disadvantages. The advantages include: having the switch controls and tiller in front of you within easy reach;
Being able to raise and lower the motor depth in the water.

The disadvantages include: the shaft and prop very close to legs and feet thus causing an obstruction to finning.
Cutting fins or waders etc with the rotating prop blade;
The motor cover sticking up in front of the stripping apron and getting in the way of the 'normal' fishing rod position;
The prop and motor shaft being in a very prominent position for a fish to wrap a line around - and also if a sinking line slips off the stripping apron.
The motor is in the way when launching or landing.

Nevertheless I did decide to explore this option to see how practical it would be in use.

The first thing which struck me was that if the motor could be tilted then some of the disadvantages could be ameliorated at least. The Watersnake ASP24 does come with a very useful tilting transom mount. This can also be bought as a spare part for between £35 and £40 and retrofitted to an ASP18. I did this for my ASP 18 - otherwise I would have designed and made a hinged tilting transom bracket out of 20mm plywood. The advantage is that the motor can be laid as near to horizontal as possible when launching / landing, and can be tilted out of the water when fishing. I can state that this system does work well and largely keeps the motor out of the way.

The trouble with most Vee or U tubes, is that the crossbar is too close for comfort to the fisherman and will also limit the amount of tilt advantage one gets from the tilting mount. On some of the more recent PVC built FT's, (similar bladderless material to pontoon boats), the crossbar is positioned in open topped rubber U clips rather than pockets on top of the sponsons. This is not an ideal fixture to take thrust from a motor, but nevertheless has to be worked with to avoid difficult and perhaps costly modifications. In my opinion, (which may not be shared by others),  extending the crossbar forwards by a foot or so, has distinct advantages and one possible disadvantage. The disadvantage is that there is increased leverage and thus weight on the sponson mounting point fulcrum position. If a frame could be designed to wrap round the sponsons to support the weight this would be a better solution. (I'm still thinking about this conundrum).

I designed and built a frame using 32mm UPVC pipe and fittings - mainly because the existing aluminium crossbar is made of 32mm pipe and the drainpipe material is readily available. To help eliminate the problem of torque rotation from the motor thrust, I made two vertical extensions to go down through the heavy D rings which are fitted half way down the sponsons under the crossbar on the Snowbee Prestige, I note that the Savage Rider and other similar float tubes have the same D ring fittings, (but nobody knows what they are for). A truncated triangular extension goes forward to take the transom mount. On my prototype this is angled downwards to give the opportunity of mounting the motor lower if required and also help the thrust push slightly downwards. 20mm plywood is used to make the transom with depressed holes to take the clamp heads and avoid the motor slipping on the transom.

The stripping apron has had to be completely redmade from some suitable netting which is velocroed around the crossbar. On mine I also had to replace the nylon crotch strap buckles because they are an unusual fit.

After fitting the new cross bar I realised that to attempt to ensure that it stayed down un the rubber U clamps, that I would have to make some backward extensions to fix 50mm webbing to, and wrap tight around the sponsons. On mine this had to be fitted to tubes facing the seat pockets, but ideally these would actually face the front of the sponson to help eliminate the lifting power of the thrust torque generated by the motor in use.

The system in use:

Getting in and out of the FT is a little like Deja Vue going back to the doughnut FT days. Because the webbing has to be tightly wrapped around the sponson It is easier to do this on dry land rather than immerse your arm up to the shoulder to locate and pick up the straps from under the FT in the water. This means that the crossbar and motor are in position before you get into the FT. Carefully step in and then lift the front and do the crotch strap buckle up. Try and walk backwards into the water as per normal, but using shorter steps. It is possible even for an unsteady old cripple I discovered. It would undoubtedly be a bit trickier in places like Elinor where you are quite deep into the water to start with.

Clear the shore, get into a depth where you can fin easily, then lift the motor to a vertical position adjust it for depth and switch on. IT works fine! Make sure you are not going to run another float tuber down or get in the way of their fishing and motor away if you wish. Otherwise tilt the motor up so the head is out of the water and fin to where you wish to fish.  Catch the fish and the motor is not down in the water for it to snag around. Believe me it works well! Is the motor case and control head in the way? Yes a little bit, but nothing insurmountable. It never bothered me overmuch - but one which was not tilted could well have had me cursing I suspect.

Is it easy to use for motoring around. Undoubtedly yes! All controls are readily in reach and you can lift and tilt the motor which you cannot do when it is mounted on the bow. You don't need to mount the switches remotely and you also do not need a complicated tiller extension - these are serious plus points.

The original reservation about catching a fin or wader with the prop is still valid. I did clip my fin twice when trying to motor and fin at the same time, as you would need to do in a strong wind. Lifting the motor higher in the water helps, but increases the wake disturbance on the water surface and I guess, (but cannot state with certainty), is also less efficient at moving the FT in the water. Moving it all further forward still would definitely help.

I am now seriously considering how a strong copper tube frame could be made and fitted to the front of a FT to use this system which would allow easier getting in and out of the water.

[fishicist]

Maybe they will be able to run float tubes on hot air one day.
Until then this may be of interest.
https://www.aos.cc/de/zeck-belly-boat-komplettset.html?utm_source=AOS+NEWS+DE&utm_campaign=95ac903592-Tackle+September+2018+DE&utm_medium=email&utm_term=0_04c671ad7f-95ac903592-72453901

[bracken]

Have made a couple of versions of this style. Works well for driving the FT but is difficult to reach motor controls and steer the 'boat'. This resulted in mounting the switches in a box on the end of an umbilical cable, and having to make a long extension tiller handle. The motor mount can be simplified by sticking some PVC 'rubber' rings, (from China on EBAY), onto the top and bottom of the bow section and hooking the transom into them before inflating the FT. (My experimental transom frames didn't alter or damage the tubes in any way; they hooked around the bow and are secured back to existing D rings with webbing). The Rider FT's would be very easy to modify to this system.

Like the idea of hot air - but worried where the burners would go!?

[Terry]

As my background, whilst working, was in engineering, I have found your Design and Manufacture notes and processes most interesting to read and applaud your trojan efforts to make it work. I also sympathise with the reasons behind it. Well done Tony. Perhaps a book would be a good idea, I would buy one, the paperback version anyway.