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

[onthebeachalone]

Here we go again! I'm making a start on conceiving the next project.

I note that there is a lot of discussion on this forum about the pros and cons of different designs, and that there is already a multi-multi-multitude of designs out there. However, I had so much fun designing and building Curlew that I really want to do it again.

I can spend a year or so designing before I need to even think about spending any money on timber or epoxy.

The critical design criterion for Curlew was to be able to go on trips with both boat and caravan. Think this one will be more a trailer boat we can sleep in either in the water, or on the trailer. (A different sort of caravan boat).

As has been tried many times before I am going to try and fit everything (berths, galley, port-a-potti, etc), into a 'pocket cruiser', hence 'Swiss Army Knife'. I'll think of a better name before she's finished.

Here are my starting design criteria -

Trailerable with existing car (2.4 lite Camry)
Buildable in existing space (roughy 5.5 x 2.5 metres.
Achievable within existing designing/building skills.
Efficient hull shape
Roomy and comfortable interior
Sleep aboard when on trailer
Unstayed rig for quick and easy rigging
Comfortable cockpit, free of boom hassles
2 berths
Stove
Basin
Porta Potti
Water Tank
Comfortable sitting headroom in cabin
Galley near hatch for ventilation and standing headroom while cooking.
Bimini over cockpit
Self-draining cockpit
Stable and self righting
Small outboard (preferably concealed in well)
Aesthetically pleasing, preferably with a hint of a classic feel.

There, that lot should provide scope for some interesting balance and compromise.

[graemet]

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

[Daddles]

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

Richard

[onthebeachalone]

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)...

[Daddles]

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

[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

[onthebeachalone]

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.

[Christopha]

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

[Daddles]

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 :D:rolleyes:

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

[onthebeachalone]

Yes, well the first boat I ever built (many years ago) was a 19' 6" bilge keeler
http://www.profitworks.com.au/wooden%20boats/ALFR2.JPG
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.
http://www.profitworks.com.au/wooden%20boats/ALFR1.JPG
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.

[onthebeachalone]

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'?

[bitingmidge]

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? :wink:

Cheers,

P

[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

[Boatmik]

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

[Boatmik]

Thus speaketh the man from the land of the forty foot tide :D:rolleyes:

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

[Boatmik]

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.

Boats of this size can get away with precious little ballast of any type. Ref. TS16 TS18 etc. If you water ballasted something like that it would suddenly start to be quite capable.


Also, obviously, the lower it is the better.For what? It depends on the criteria. And reading the list at the top you are not asking for it to be ocean crossing capable.


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.Generally centreboards and dropping keels have to be really heavy to make meaningful contributions to the stability of the boat - but ballasting them to this extent results in making them very hard to get up and down.

Also you have to design to the worst case scenario - if the boards can be retracted then a gust will hit when they are. So perhaps they are less effective than just having a lump of lead just under the middle of the hull. Have a look at Bolger's Micro and Oldshoe for shoal draft arrangements.

Or the later versions of the NIS for ballast slung just under the bottom with the centreboard going through.

Or Oughtred's Caledonia Yawl for relatively light bilgeboards.

All of these boats have large contributions to seaworthiness made by the "reserve buoyancy" of the hull. If you imaging a boat knocked down on its side - if it is high sided with a not too big a cockpit that means the centre of gravity has to be very high up to make the boat roll over further. Whereas if the boat is relatively shallow in hullform most of the hull volume will tend to be lower than the centre of gravity and the boat will continue to invert.

Say you take your Curlew and build the sides up 4 ft and fit decks. Then if she gets knocked over she will be very happy lying on her side and will have no tendency to invert. With the original hullform of curlew and an enclosed deck she only has to roll over a bit further than 90deg to roll over completely.

Stability is about much more than ballast alone.


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 gravityIt can be a good idea to reserve some of the lead as internal ballast - maybe a hundred pounds or so if you don't do a full analysis of how the boat will float (working hte weights and centres of all the bits in a spreadsheet) which is what you have to do anyhow to get some idea of the stability using various formulae.

Whether you end up putting the lead internally or hung close under the hull or hung a coupla feet or so below the hull in a shoal keel or put in a dropping keel or ...

... ways of stopping it moving around in an errant manner should be pursued.

MIK

[Boatmik]

Cutting big slabs of lead - oxytorch.

[Boatmik]

By the way - I am trying to be careful not to stipulate specific ways of dealing with things on the boat - I will try to add information that broadens up the thinking where possible.

Best wishes
MIK

[mark_dugong]

I thought the following might be an interesting addition to this thread as well as providing me with a few hints.
Out of curiosity,has anyone seen any "Paradox" micro cruisers which are micro coastal cruisers designed by a Matt Leyden. These small (14 ft) cruisers have even cruised to the Bahamas which seems remarkable to me for a 14 ft yacht.
Now, besides being such remarkable little vessels,they seem to resolve their lateral resistance problems with bilge runners,which are narrow horizontally extended wooden keels from the bottom of these flat bottom yachts-here is an interesting link
-http://www.microcruising.com/-
sorry I don't seem to be able to make a link but that is the website anyways.
What I am interested in, is can these bilge runners replace my somewhat cumbersome (but workable) leeboards on my lightly modified 25ft. Jesse Cooper of Bolger design?
Thus saving me some work in tacking and adjustments underway as well as losing two ropes.
Mark

[Redbeard]

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
I've been lurking here for a little bit and thought I might be able to point to an idea here.

Gavin Atkin (Pommie bloke, amateur designer) has a design called "Bluestone", a pocket cruiser, available from Duckworks for free.

http://www.duckworksbbs.com/plans/gavin/bluestone/index.htm

I know, when it's free you probably get what you pay for but he has some interesting ideas. My main reason for posting about it is he uses twin bilge keel centreboards as proposed earlier. Also, it wouldn't take much to reduce this boat to the size needed for the available work space.

[b.o.a.t.]

Here we go again! I'm making a start on conceiving the next project.

I note that there is a lot of discussion on this forum about the pros and cons of different designs, and that there is already a multi-multi-multitude of designs out there. However, I had so much fun designing and building Curlew that I really want to do it again.

There, that lot should provide scope for some interesting balance and compromise.


Murray Isles "Chestnut Teal"
http://www.islesdesign.com/designs/menu.html
doesn't seem to miss much off the wish-list.
could be a good place to start.

Or maybe take a TS16 out-of-class?
cheers
AJ