Tender conversion to sailing

solent clown

solent clown

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Having posted on another thread about the possbililty of towing a sailing dinghy, then deciding that towing would be simply too involved and complex with too many opportunities for mishaps I have decided to actually go ahead and build a conversion subframe to allow us to try and sail our inflatable dinghy. I have designed the frame, and will make a steel prototype tomorrow for testing (should it actually work I will go for either stainless or aluminium)
The onlt part that really had me scratching my head was the lee boards. I cannot stick a centrebaord in as it is an inflatable vee hull. So I plan to run a transverse tube with a leeboard on each end, this will run through two plastic bushes and have a simple handle in the centre to raise and lower the boards, Is ther any real reason I cannot just use the one shaft and raise or lower both together? It is never going to be a racing machine and need not look too graceful. I have no experience of using lee boards hence the ask.
The mast will be stayed within it's own subframe which will also carry the cleats for the jib etc. The flubber itself will be "largely" unstressed except in compressiom if I have this subframe right.

I have left the keel deflated for ease, so pics just for fun mock up. .
url=https://flic.kr/p/MGemmy]
29991319328_2e15a2e38e_b.jpg
[/url]IMG_20180805_131612 by mark punksteel, on Flickr

IMG_20180805_131933 by mark punksteel, on Flickr

IMG_20180805_131958 by mark punksteel, on Flickr

IMG_20180805_131915 by mark punksteel, on Flickr
 
As well as the leeward lee board being deeper in the water on a hull which heels, it's also braced against the hull.
The windward board will only be held by the pivot and the force of 'lift' from the water will probably break it?
Also if the two boards are not pretty much parallel (or some subtle ideal toe-in, toe out?), then there will be lots of drag.
 
According to Michael Green in his book ‘The Art of Coarse Cruising’ there is nothing faster than an inflatable dinghy sailing down wind when you have lost your oars/outboard.
 
lw395 said:
As well as the leeward lee board being deeper in the water on a hull which heels, it's also braced against the hull.
The windward board will only be held by the pivot and the force of 'lift' from the water will probably break it?
Also if the two boards are not pretty much parallel (or some subtle ideal toe-in, toe out?), then there will be lots of drag.
Click to expand...

I will bear all that in mind, thanks chap. If I cant make them strong enough that will make things difficult. best plan may to put 90 degree bends at each end of the tube and support the leebaords all the way down, but that will also create drag unless I make a complicated foil shape out of two stainless or ally sheets.
So you think two seperately moveable boards would be a better plan?
 
solent clown said:
I will bear all that in mind, thanks chap. If I cant make them strong enough that will make things difficult. best plan may to put 90 degree bends at each end of the tube and support the leebaords all the way down, but that will also create drag unless I make a complicated foil shape out of two stainless or ally sheets.
So you think two seperately moveable boards would be a better plan?
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why not mount them both on one tube but offset them by 90degrees - one down the other lying alongside the tube, or even 180 degrees of offset if they're not too long. Thinking about it, an angle somewhere between 90 and 180 may be best all round solution.
 
greeny said:
why not mount them both on one tube but offset them by 90degrees - one down the other lying alongside the tube, or even 180 degrees of offset if they're not too long. Thinking about it, an angle somewhere between 90 and 180 may be best all round solution.
Click to expand...

brilliant! why didnt i think of that, well done! I will go with that idea. many thanks
 
greeny said:
why not mount them both on one tube but offset them by 90degrees - one down the other lying alongside the tube, or even 180 degrees of offset if they're not too long. Thinking about it, an angle somewhere between 90 and 180 may be best all round solution.
Click to expand...
Good idea!
I'd say a bit more than 90deg, as one will have to point forwards when not in use and you want it clear of the chop. Would also allow a bit of raking to adjust weather helm.
 
Top section of the subframe on CAD. To save time I am using a tube bender rather than the ring roller, basically that means the tube is bent around a certain point instead of a long curve. if this works I will ring roll the curves to the exact profile of the flubber tubes

IMG_20180813_163419 by mark punksteel, on Flickr

In raw steel for test fitting, the leg on one side is left long for a reason i will explain later.

IMG_20180813_170624 by mark punksteel, on Flickr

IMG_20180813_170631 by mark punksteel, on Flickr


IMG_20180813_170638 by mark punksteel, on Flickr


there will be a hinged flat bar shaped to the tube to mount to the eye on the bow.

IMG_20180813_170701 by mark punksteel, on Flickr


experimenting with potential bracing of the upper section. belt and braces for steel, but in ally probably needed

IMG_20180813_171355 by mark punksteel, on Flickr


IMG_20180813_171355 by mark punksteel, on Flickr

Lots more to do, the floor section to create the "box" and the mast step, then the transverse bearers, bracing to transom, leeboard setup. I should have it pretty much mocked up ready to weld by lunchtime tomorrow, honest guv'
 
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could you explain that further about the leebaord, I cannot quite picture what you mean.
As for ballast weight, maybe if I work out the volume of the inflatable vee keel it could be filled with water instead of air. Probably be way to heavy though, and half full would be a sloshy nightmare of doom. Still worth a look
 
I suppose another way to ballast might be a bladder we could fill with water attached the lower section of the subframe. I am also unsure how much sail to use, we have several mirror setups, so will start with those. It will have a jib as well as a main and will be a gaff unless we can reduce the sailplan enoigh not to have to bother.
I have no idea how it will sail. Obviously it is going to be a huge compromise and no racer, but we want it to be fun and able to move and manoeuvre...
 
So far I don't see any provision for a mast step. Presume it is on the way? Some sort of triangulation with the shrouds? to take the compressive load..
Re the lee board, a plank across the boat (doubles as a seat) with braced bits going down at the ends (curved braces following the tubes) then use one lee board and have a hook/something, that allows you to drop it on the lee side when tacking. The bits of braced wood will take the load, if it is secured at the top. Bit wordy this, a pic would be much clearer....
 
DownWest said:
So far I don't see any provision for a mast step. Presume it is on the way? Some sort of triangulation with the shrouds? to take the compressive load..
Re the lee board, a plank across the boat (doubles as a seat) with braced bits going down at the ends (curved braces following the tubes) then use one lee board and have a hook/something, that allows you to drop it on the lee side when tacking. The bits of braced wood will take the load, if it is secured at the top. Bit wordy this, a pic would be much clearer....
Click to expand...

mentioned earlier that the step will go into the lower section of the subframe. shrouds will have their own transverse frame attached to the main subframe.
Yes a pic would be clearer, do me a sketch if you are up for it. Any input gratefully received. You dont need to be an artist, I am well used to looking at clients sketches :encouragement:
 
Homer J said:
Wouldn't it be simpler (and cheaper) to use a couple of these? You could use the oar on one side as a lee board?

https://www.ebay.co.uk/i/162569192960?chn=ps

Or perhaps I am missing the point (and ruining the fun)
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never seen those, clever things. But yes, you are ruining my fun. It would be good to at least try to make the flubber actually sail. That thing you posted the link to might make a fun little spinnaker for it though! Maybe run two as a cruising bra :encouragement: We will look like a pair of tits in this contraption anyway so might be quite apt
 
When's the maiden voyage ? We might in OV soon so just wondering if that's the practice area under the bridge or you are planning long trip? You could just cannibalise an Oppie ?
 
ashtead said:
When's the maiden voyage ? We might in OV soon so just wondering if that's the practice area under the bridge or you are planning long trip? You could just cannibalise an Oppie ?
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maiden voyage might be friday if I can find the time. If not then probablySunday afternoon. Yes will hopefully be under the bridge. Wave if you see us, or come rescue if you hear us call on the vhf!

As for cannabalising an oppie, this is going to be a zero cost build as I am using scraps and offcuts. Rig is going to be a cut down mirror set up as I have several laying about too. If I had oppie bits it would have been perfect
 
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Might not be that soon I'm afraid as planning to travel west in week if weather permits. Looking for quiet waters to venture in blow up canoe once moored up though so might not be that much help in any rescue
 
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