Making a displacement rowing dinghy plane

Hi,
I've got a little fibreglass tender here about 10.5 ft long.
It's a standard kind of rowing thing with a moulded in keel, except it's really, really light weight. I'd say 35 kgs. Which is why I'm keeping it in a slot I have in the village dinghy park here. Security is awful so it can't be worth much! I've taken stuff like the steel keel strip off it to make it light as possible for easy hand launching. And also painted it in multicoloured dazzle camouflage a la Peter Blake's Mersey ferry from a few years back- but that's another story. Another story mainly about what to do when you've got 13 tins of old yacht enamel left over each with an inch of paint left in the bottom.

Anyway, I'm keeping it to use on the river here and on Southampton Water in calm evenings in the summer and would like to make some forays up beyond hull speed. So I can get a bit more distance covered and get to more fishing spots.

I have a selection of outboards, long and short shaft., 2.5, 4, 5, 8 hp. Two and 4 stroke.

I'm thinking either the 8 hp 2 stroke or the 5 hp four stroke. The latter is exceptionally good on fuel, and pretty quiet which would be a bonus.

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I weigh 90 kgs with 10 kgs of fishing gear etc, and propose to use the boat one up.

So I need to do something with the tuck at the stern and end the coanda misery. I'd like to make it a slip on appendage, moulded onto the upturned hull, then it can be removed with a couple of bolts so I can also row it (what it was designed for in the first place!) I don't think any appendage would weigh very much, as it would be supported, nested by the hull above it so will be 3 mm ply, sheathed with glass and epoxy. I reckon 10-15 kgs.

My rusty memory of planing theory, mostly read on here is flat section, 4 ISH feet wide. Maybe a hook to the surface aft or a vertical interceptor, but how much hook, how deep an interceptor?

Any ideas or photos on what works? Must have been done before?

I'd been thinking Sea sled/ Uffa Fox Hydro-Skee type approaches, but maybe that's over complicating things and I just need a flat arse end faired into the hull roughly amidships and sealed forward, just open to drain at the stern, ie., Long Flaps either side of the moulded keel. Or sat on the keel then splitting forward and faired into the bilge flats amidships?

I might give it a curved outline at the stern, as I experimented a lot last year with windsurfing boards underneath an inflatable tender and this shape makes it real fun to stand in the middle and foot steer the thing- basically you're surfing- a great laugh! Killcord compulsory though!

It also means I can be away from the engine further forward for trim and not have to rig up steering! More weight saved.

I don't need sending a jpg of a guy in a Popeye hat on an upturned table... But I suppose this wouldn't be boat design. Net if nobody sent me THAT jpeg.

 

I love that psychedelic camouflage colour scheme!
It will certainly make a statement when you are pottering (or speeding like a bat outta hell....... ) on the Hamble River.
Have you tried it with the 8 hp motor, and an extension tiller that will allow you to get your weight right up into the bow?

 

Maybe it could fly on foils that could fold up or be removed for rowing?

 

Foils are too much work! I've made too many 'foiling' boats that don't foil to go down that rabbit hole again.

Turning it upside down, covering it in mould release wax then laying up a flat surface about 4 feet wide on the back end is more my level, plus I want it on the water for the spring- which includes fitting out and painting the inside.

Re the 8hp and a tiller extension. No, I haven't tried that but I imagine it could probably plane one up. But not in a nice way!

I did something similar with a 470 racing dinghy hull some years ago with a tiller extension and the 5 hp four stroke. Yes, it planed, but very stern down no matter how far forward I went due to the tapered stern, a 470 is after all a planing dinghy so it sort of worked. It felt like it topped out at about 9 or 10 knots though. A lot of noise and spray. Not as much forward motion as I would have liked either!

I want to do something a bit smarter this time.

One idea I had overnight was to continue the bilge runners aft into bat fins . The runners are parallel. 80cm apart so maybe a tad narrower than optimal.
I could very easily draw a straight line from the highest part of each bilge runner (with boat upturned) parallel with the main keel. Then cut two vertical plywood hull sides, tapered to nothing at the front and bolted through my bilge runners which are solidly laid up inside the boat.

I could screw some lengths of u shaped aluminium or uPVC extrusion into the outsides of the main keel and the insides of my bat fins.
Then I could lay up some flat panels of plywood with carbon either side taken to a feather edge at the bow end that slide into my extrusions and meet exactly with the curvature of the hull at the front edge!

Slide the panels in for motoring, out for rowing! They would be, like 2 X 2 kg panels!

Little clips at the stern to stop them falling out would be a bonus. I could continue them past the stern at the sides into longer trim tabs, leaving a vee out the middle for the motor, like they do with the dropstitch floors of some modern inflatables to give more lift at the stern. Might even be able to sit at the back and steer then!

I can then motor with and without them- see what difference it makes. Though I do also wonder what the bat fins on their own would do- they would stop all the lateral outflow of water at the bilges aft, so might do a lot on their own.

At the the front feather edge where my panels meet the hull I can half glue a 50 mm strip of pvc or hypalon. So the back 25 mm of fabric isn't glued to the hull, and due to the curve of the hull and fabric stretch, will roll back on itself, then slide in the feathered forward edges of my planing panels, then snap the strips back over. Will stop any problems of the panel leading edges coming away from the hull.

My extrusions on my bat fins can be mounted a cm or two from the edge of the fins. Really stop that outflowing water from progressing round the corner.

I could move the extrusions to experiment with different deadrise, although I'll certainly be starting with 0 degrees.

I think this edge plate effect, (constraining the water- forcing it to move in a stricter fore and aft only direction) that is one of the reasons for the low power efficiency of things like sea sled and hydro- skee.

I wonder should I give my panels a very slight amount of rocker? Or a bit of hook at the stern? How much?

 

I dare say it would be easier and quicker to just build a new boat of similar size designed for planing from the get go. Something like Selway fisher Little Harrier, which seemed to be a copy of an old Monk design..

 

A firefly dinghy has pretty similar lines and they plane in the right conditions. Have you tried sticking the 5hp motor on it as is and seeing what happens? You might want to jam a length of PVC pipe on the outboard tiller so you can play around with trim by moving your bodyweight forward.

 

I am thinking I need to write a parable about a guy that takes in a stray dog. He cleans and grooms and trains it until one day they win best of show. Filled with confidence that he can do anything he puts his mind to, he goes to the vet to inquire about surgery, "I think I want a cat".
Those sweet convex curves will be pulling you down if you leave them in the water at the speed you want to go.
I have been thinking the other way. If I design a super-efficient plaining little sea sled, can I make it convertible to a reasonable performing displacement craft with hull appendages?

 

What kind of appendages? A loaded down planing boat naturally becomes a displacement boat, but usually too draggy to be a decent rowing boat.

 

I don't think it would be quicker to build, and it certainly wouldn't be cheaper- though it would likely be a better boat than the contraption I'll end up with. I just looked at the Little Harrier- it weight 39kgs and takes up to a 20hp engine they say. It's quite similar to a Mirror at first glance, but looks like it lacks the Mirror's rocker aft of the centre, which would make sense with it being a motorboat design. It would be quite a handful I'd imagine with 20hp. When I was a kid, I had a plywood Fireball dinghy, the back half of which had been set alight in the boatyard by a local miscreant. It was abandoned and floated up and down the beach for a year, gradually having its stainless fittings unscrewed under cover of darkness. Then someone cut the charred back off it, glassed a transom in and gave up on it, eventually leaving it back on the beach where I happily rescued it. It used to plane HARD with my Dad's old Jonson 4, although I probably weighed 45kgs back then.

Problem now is I had 13 boats at the last count and can't own any more- because they hardly get used and there is nowhere to put them. But a couple of slide in plywood panels for an existing boat- that I could justify- plus I have all the materials for that job as excess from other previous jobs. Plus, while I'd imagine it must have been done, I've never seen it done, which makes me much more interested in doing it. This multi-coloured ridiculous contraption will be MY multicoloured ridiculous contraption! I have no idea whether it will work, but it's probably only a couple of weekends to find out! I wouldn't have the spare materials (or the time) to build a whole boat from scratch.

I'm planning all sorts of things with this hull this summer (time permitting). The hull was free and I just see it as a development mule for some of my ideas (and magazine articles I write about these adventures to (barely) offset my materials costs). Also on the list is making it into a pedal boat- or pedelec to be precise- not as hard as it sounds as I've bought a kayak pedal drive off Alibaba (Vicking Kayak) - just need to epoxy in a chest for the drive- plus a few wheezes I've come up with for the pedal assist. (Obviously not planing with 1500W+ puny human, and I'm totally off topic now but I am convinced that pedal assist small boats WILL be a thing. Or I hope they will be for me anyway.)

 

In that case, take a look at the "tango skiff", and maybe you can graft on some similar plywood extensions. I built a modified D18 dinghy (morten Olsen), that would plane at 18knots with 15hp, but also sail pretty well for what it was. Cross over boats will always be a compromise.

 

Tlouth7 suggested you fit up the outboard and give it a go for starters.
This is a good idea, to establish a baseline to work from.
From there, it would be easy to experiment with the interceptors by clamping plywood panels to the transom.
Your boat is very obviously not meant to go fast, and may become unruly if it does, so do wear a life jacket while experimenting!

 

You make a good point. I was thinking of reconfiguring the whole of the back end of the boat. But adjustable depth interceptors would indeed be a more sensible starting point and might make enough difference on their own.

Got to fix the transom and other woodwork first or no engine will work on it!. Our early spring warm spell has ended with rain and cold here though. So too cold again for epoxy!

 

No magic other than the magic of lowered expectations. Just a hull extension from the sharp immersed transom smoothly back a few feet and a couple inches above the surface.

I can totally relate to Jakeee's too many boats problem. That hull of many colors will make a wonderful pedal craft. I wonder if two could pedal facing each other coffee grinder style.

 

I could have two facing each other but decided against it. I've opted for a single person, but with 1500W pedal assist motor for a bit of help. I have two of the cheap Chinese pedal drives, or I could ( and this would be more efficient) just link the two sets of cranks through one of the drives. I'd need a pair of cogs if I wanted the rearward facing crew not to have to pedal backwards, unless something can be flipped in the drive leg (unlikely), or it might be ok to pedal backwards - I'd imagine it would produce less power and feel weird though. Would be interested to set this up and find out some day. But I'm not doing any of this. I have something rather more exciting planned.

The Vicking Kayak drive unit comes in two versions, one in cast aluminium ( with vaguely faired profile leg) (the one pictured here).

The cheaper version with an aluminium tube for a leg, currently in my loft, looks to be (I haven't had them apart yet) the same internals. I think this is the better way for me as weight is everything, the tubular leg is much thinner and I can fair the tubular leg myself with foam and epoxy for a lighter leg with a proper NACA foil shape.

I'm actually transom mounting the leg for a variety of reasons, so my 'trunk' will be a drop in system at the transom, which will be liftable, adjustable height, although not steerable due to chain drive, unless I fit a steering tab at the back of my leg (on the shaped leg drive), or make the whole faired cover rotate, sleeved over the tubular leg. I might end up with small, lifting twin rudders either side of the drive. I don't want to be where the drive is. Certainly don't want to cut a trunk in the middle of the boat. That's hard to revert if it doesn't work out.

I bought both styles of Vicking Kayak pedal drive ( plus their fake Hobie Mirage Drive- the pedal drives are fakes of a US built kayak pedal drive too!). I hate bankrolling the Chinese like this, but lots of boats to develop with limited funds, what else can you do? I wanted to a) see if they are strong enough for electric auxiliary power and b) the photos were terrible on Alibaba, so didn't really know what they were going to be like. C) see what the duty and extras worked out to be.

They are actually a bit better than I thought they would be- the stainless does appear to actually be stainless, for example. The three drives with all the duty, shipping etc to the UK cost about £900 in total.

Eagle eyed readers might have spotted the aluminium hinge supports on the transom.

It will be illegal and impractical, but it will have fold down wheels that will rotate down to the balance point and a fold out tow hitch for my ebike.

I think you can probably guess where I'm going with this. Tow the boat down to the water, chuck the bike in it. Whip the quick release back wheel off and clip it into the new QR hub and sprockets already fitted in the boat, that are chained up to my drive leg. Front wheel sits in hydraulic steering plate, bike straps and clips in place, so you sit on the bike pedaling and steering down the river. Paddle for reverse!

I originally looked at a rolling road system, all adjustable so any bike clips into the boat and drives it away in seconds.

It's all an evolution of an idea I had when I was a kid called 'boatorcycle', involving a CBR900rr, a jet boat hull with a fold down ramp at the back of it so the motorcycle could be ridden in, clipped into the rolling road- happy days - 150 hp jet boat with 6 forward gears, jet bucket for reverse. It was a partially a protest at the fact that a 150 hp motorbike, used, was lower cost than a 150 hp outboard, yet came with a gearbox, wheels, brakes, tyres and generally a **** ton of cool technology and engineering that the outboard didn't have!
And later car/ Landover powered landing craft type variants for commercial marine or military, but I've got to start somewhere! None of those got built, but this one will.

The rolling road PTO is cool, but quite heavy and too draggy for a bicycle- especially a mountain bike with knobbly tyres.

I did some experiments and the back tyre doesn't slip if bolted down VERY hard to the rolling road drums, but it gets very hot very fast, plus has to be massively over inflated, which means you get no grip on the beach. You could take a pump and raise and lower pressure, but it's an extra step. Quicker I felt to just swap a quick release rear wheel over and stow the bike's rear wheel up forad in the boat. I'll make a little waterproof locker or bag for it. Less to go wrong with chain drives, less transmission loss, but it's not so much in the spirit of 'boatorcycle', losing the rolling road but that's something I'll live with.

There are other aspects/ choices/ compromises like this. To do this most effectively in terms of power, speed, lightness I would actually be miles better off having the motor at the prop like all small electric outboards, just having somewhere aboard to STOW the bike, just use the bikes 52 volt battery to power the boat. Just unplug the bikes battery and slot it into the boat. Plus epropusion motors are already 48 volts so that would be an easier way to go.
But I want to sit on my bike steering down the river and I also want pedal assist. I think others will be the same. When ebikes get even more powerful, the pedal assist will become even more pointless, plus such bikes probably won't even have pedals. But I, for one like to get a bit of exercise on the water, plus the idea ( in future with say 4kw with power assist) of planing down the river in what to other boaters appears to be a pedal boat just massively appeals! It's not like you see pedal boats EVER anyway in this country. Let alone electrically assisted, amphibious ones that towed themselves down there!

It's not going to be for the shy person, especially with that paint job. Thank God I live in a country without compulsory boat licensing, insurance etc. The harbour master won't like it, but all he'll be able to do is watch and take photos.
You can see in the attached images how I have attached a sprocket to the crank square drive. I just cut down a spare bicycle crank and welded and bolted the sprocket onto the crank stub. Then covered it all in epoxy to hide the mess and stop my weld rusting. These engineering aspects are the hard bits for me. I've got decent boatbuilding/ composites skills but am struggling with the rest.

I'm going to do it all at this level of 'engineering'. I want it to be something any one else can build with similar hand tools and DIY skills.

The pedal drive was about £250, the bike bits were free, off the many bikes I pull out of hedges and with 'please take' signs in people's front gardens. The boat was free. Bit of epoxy, few bits of marine ply offcuts I've got lying round. Bit of time and effort and creativity and anyone can make a jaw droppingly awesome pedal boat that's ( to my knowledge) unlike anything anyone else has ever done. The ebike stuff obviously adds cost, but no reason for someone to not give it a go with a non electric bike. Wouldn't beat any speed records on the road or on the river though!

The empty boat, wheels etc. will weigh about 60 kgs I think. I reckon that Kona in the background of the earlier pictures ( free- found discarded in a bush due to the rapidfire shifters requiring a spray of oil!), would move it in first gear even up small inclines, albeit at little more than walking pace.

The DAY I saw my first ebike about 15 years ago I came up with this, and finally I've gone freelance at work and can now work on such schemes of which I have countless others.

Much more powerful ebikes will come soon and for when they do I'd like to have my folding, legally trailerable version available. That planes. Or foils. I've got the plans! This is just a test mule for the propulsion system, fast drop in of the bike system etc. To test all the systems I need something that will simply float, not roll over etc. However, I will thoroughly enjoy progressing slowly through the village towing this monstrosity.

Always wear a helmet. And a lifejacket.

Anyway, this has gone off topic. My other aim for the boat is to take it fishing etc with an outboard- hence my original posting.

Ps. It is possibly patentable, but I think it's too niche to bother with, plus it's pretty obvious and someone somewhere has probably done it. You only need one person to come out of the woodwork with prior art to make any patent a waste of money. The later, folding version that will plane/ foil and be legally trailerable due to a more road friendly width has more specific protectable aspects that could stop anyone else doing it as a sellable proposition anyway. (Though I note a guy on Kickstarter did OK with a dreadfully compromised camper, bike trailer amphibian that leaves it's wheels down in the water and looks like it will max out at 2 kn, though it would be slightly safer than mine on road) The one I'm working on now is development for the next one and also a lot of fun. I'd love someone else to build one also. All the key info is above, and I can provide other info I've worked on from trailer linkages to bike clamping system to corrosion protection, lightweight steering mechanism that adjusts between different bike wheelbases etc etc.

 

I like the colour scheme!

I have a lightweight 14ft skin on frame rowing boat (picture somewhere on this forum) with an electric DIY outboard. At 1500W it puts its nose in the air and drags a substantial wave behind it so I am also planning to try to make it faster but not necessarily planing at this full power level. My plan is an aluminium delta plate attached to the skeg, with its tips supported by thin struts to the hull. I've seen this on double ended fishing boats in the Med (but not in action) . I think this would be an easy first option for your boat. At low speed the plate is about level with the flow and at higher speed the boat trims bow up and the plate has positive incidence and lifts.

The alternative I suggest is a cross between trim tabs and your original suggestion: four trim/planing surfaces, two each side of the skeg about 18" to 24" long and hinged at the front (divided into four because of the curve of the hull) and projecting past the transom so they can be attached to manual or even electric actuators. I'll leave you to resolve the hinge and actuator problem!