Thread: S.A.K. (Swiss Army Knife) Boat

Geez, yer don't want much, do yer?
If you're going to build it inside a 5.5 metre space, it can't be much more than 5m LOA, so with comfortable headroom inside - standing yet? - and all the other stuff you want to cram in, you will have a task getting your last requirement.
Good luck,
Cheers
Graeme

It's alright Graeme, him and his wife are both about 3' tall

Richard

I reckon if a use a building frame with wheels I can move her out a bit when I need to get to the innermost end (haven't yet figured whether that will be the stem or the transom). Problem is that the drive slopes down a bit from about 4m in front of the garage door. I'll need a restraining rope if I'm not to end up with a pile of splintered ply on the roadway.

Weight will be critical for towing, and presumably a lighter boat can live on a lighter trailer, a further weight saving. Water ballast needs to be considered early as it will have a big influence on design and construction method.

I'm looking into that one (for about the fourth time)...

Water ballast takes up more room than lumps of lead. Dunno that you're going to be able to spare much. Maybe a steel centre board such as David Payne uses - puts the weight lower in the water so you don't need as much.

Richard

It's hard to get enough weight into a centreboard without it becoming really hard to pull up.

If it is pivoting and you don't want the wire trailing in the water and don't want it intruding into the interior too much you are always working at a serious mechanical disadvantage.

MIK

All of which is complicated by the fact that I was thinking an offset centreboard might help keep the cabin clear of obstructions. That thought led me to wonder if TWO offset centreboards might be worth playing with. One on each side built into the front edge of each bunk.

I've got a lovely big chunk of lead (the keel from an abandoned restoration project). My first thought was to use some of it to balance a single off-set centreboard, but the more of that sort of weight I add, the heavier the construction (and the trailer) must be.

Thanks for the feedback. I'll keep playing around, do some experimenting, and no doubt kepp this thread alive for a looooooong time.

What about bilge keels? reduce your draft, no intrusion into interior and she will sit flat when the tide goes away etc.

Originally Posted by Christopha

What about bilge keels? reduce your draft, no intrusion into interior and she will sit flat when the tide goes away etc.

Thus speaketh the man from the land of the forty foot tide

He has a point though. Bolger, the man who makes practicality work, has often used bilge keels and leeboards ... and you can certainly do a lot worse than plagiarise Bolger.

Richard

Yes, well the first boat I ever built (many years ago) was a 19' 6" bilge keeler

which had two steel plate bilge keels PLUS about 230KG of lead on the bottom. She lived on a mooring. It was great being able to let her dry out on the beach.

I think bilge keels would make the whole trailering thing a bit more difficult but they certainly leave the cabin clear. I recall that it was quite tricky getting her on a trailer in a breeze. Accommodation for the bilge keels reduced scope for anything much in the way of guide rollers etc. Worth considering the option though.

I guess the weight is there anyway whether the keels are retractable or not.

My son shouted me a "Red Ballon Days" trip on (Alan Payne designed) Solo for my birthday. Birthday was in February, but the trip as yesterday. Well, the crew did all the work so I had nothing to do but chat to the other passengers, and reflect upon off-set centreboards, bilge keels, water ballast etc.

Came to the conclusion that Daddles is right. Any useful amount of water ballast would take up too much room. To be effective the ballast must be someting with MUCH more dense than water.

Also, obviously, the lower it is the better.

If I use steel, twin, 'off-centre-boards' in which each 'off-centre-case' is also the front of each settee berth I preserve cabin floor space, achieve balance, and get most of the weight really low, below the bottom of the hull.

Remaining ballast and trim requirements could be satisfied with moveable blocks of lead. Now, I have this nice lead keel, practically immoveable due to the effects of gravity. It is about 1500mm long (see picture below). I've had some experience collecting, and melting, scrap lead and moulding a keel like this. I wonder if anyone has any bright ideas about how to reverse the process and convert this lot into lead 'bricks'?

That may be a question better for the metalwork forum. I'd guess that not too many of those blokes pop in here too often.

It's a bugger of a thing to cut up, maybe an oxy would be the go and you could catch the drips and have one ingot before you melted the rest?

Cheers,

P

Originally Posted by Boatmik

It's hard to get enough weight into a centreboard without it becoming really hard to pull up.

If it is pivoting and you don't want the wire trailing in the water and don't want it intruding into the interior too much you are always working at a serious mechanical disadvantage.

MIK

Sorry - you have headed off on a tangent because I didn't explain myself.

You don't necessarily need a lot of weight in a centreboard to hold a boat this size up.

A modest amount of internal ballast or ballast in a shallow or very shallow keel works well.

MIK

Originally Posted by Christopha

What about bilge keels? reduce your draft, no intrusion into interior and she will sit flat when the tide goes away etc.

Bilge keels are very problematic as far as sailing goes - they result in way too much wetted surface - I've never seen a bilger keeler sail really well unless they were retractible - then you can go as simple or high performance as you like just by working out area and leading edge length.

But still probably need to retract if you want really good sailing performance.

MIK

Originally Posted by Daddles

Thus speaketh the man from the land of the forty foot tide

He has a point though. Bolger, the man who makes practicality work, has often used bilge keels and leeboards ... and you can certainly do a lot worse than plagiarise Bolger.

Richard

Bolger may have a boat with retractible bilge keels, but I am not aware of any with permanent.

Leeboards are the simplest way of having retractable bilge keels. But as he says ...

Yes, they do need to be that big
And they do need to be that long
and they do need to be that heavy
and the supports do need to be that strong

MIK