Low-speed sailboat hull

Short replies

I doubt if there is really room for your forward crew. Sail area may be too big

Normally you have a longer bottom rudder pintle than top one, which makes it easy to fit even a fixed rudder when on the water. The lifting tiller as you have drawn is very common. If you hinge the blade at the top forward corner pulling the tiller forwards will lift the rudder

Go for the expensive ply

5kgs is plenty, you need about 2kgs on a Duo

Yes you need a skeg. I would fit a transom knee for the rudder support, unless you promise to never, ever to run aground.

Mast dia sounds OK, you'll need a stronger boom at the gooseneck end

6ft oars should work OK and are easier to stow (probably sticking out the bow)

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Don't be silly. Make it at least 10mm. You're being too theoretical. 0.0005 mm is nominally an offset, but inadequate in practice.

If the reinforcement is pieced up as the image indicates, it'll be useless. Put a continuous piece of timber across the top. Something like 40x20, with the 40 horizontal, would be a good place to start.

Seems undersized to me. Lug masts should be stiff, not flexible. At a rough guess, 75 mm sounds better for 8 m² of sail with a fairly high aspect ratio.

No. Read Skene's.

Yes.

You can get by without a skeg, and not having one would be an advantage for light weather sailing. You may need the rudder partially down to help tracking when rowing though.

 

Well, there isn't a lot of room, but a person can fit there. I will try to make some kind of mock up in my room (with random stuff) and enclose myself in that volume for some time. I'll report if that's comfortable enough

Well, these pintles aren't available in various lengths. I'm just happy I found any kind of pintle.

Lifting the rudder isn't the problem, it's getting it down... But I'll add the line you described.

How much of these 5 I'm likely to use on such project?

Do I really need such long oars? The ones I've shown in screenshot are 1.5m (3ft) long. The blade is in the water at any position, and it is comfortably reachable by the rower. They fit inside boat too.

Guys, whom I am to believe?

Ok, I just have to check the exact dimensions of these hinges. I just saw them in hardware store, but didn't exactly measure.

Like this?



It is 40x20, but looks way oversized to me. And there is no support for lower rudder hinge. Did I understand you correctly?

P.S. With some luck, it seems, I may get away with only 3 sheets of ply: 2 sheets of 4x3050x1525, and one sheet of 6.5x1500x2500:

 

I don't think you really mean 3ft oars, that's as short as a canoe paddle. Have you seen this?

http://www.sailingcatamarans.com/index.php/designs/1-beach-cats-and-dinghies-/430-one-hand-paddle

which is what I would use when sailing.

If you left the rudder partly down and lashed it then yes, you don't need a skeg. But the tiller may get in the way so why not make life easy and add the skeg?

I agree with noeyedeer, go for a bigger section mast, and boom, I'd forgotten how big your sail is (bigger than a Laser). One reason why I doubt anyone will sit in the forward position, unless you really do only sail in very light winds (or at high altitude), say under 8knots wind, over 1500m high, is because your boat is very overcanvassed and your crew will need to be actively balancing it

Holding a rudder down is no problem with a downhaul rope.

This is a good page for very basic rudder systems on slow boats

http://www.boatbuilding-links.de/Jim-Michalak/kickup-rudder.htm

but the single sided rudder check idea is horrible, very weak and no lighter than a conventional stock

You can always make your own pintles with a vertical bolt into a plate - that's what I have on my own Duo dinghy

Richard Woods

 

Oh, sorry. I got lost in conversion. I meant my oars are almost 5 feet long.

I looked at the link you gave me previously, and I'm sorry, but I still don't grasp how having a skeg helps keeping rudder down. Could you explain in other words, please?

Yes, my boat is intentionally overcanvased, because I expect to sail in very low winds most of the time. By my calculations, 2 person crew should be able to keep the boat upright without sitting on deck in winds up to 9.7 knots. In any but lightest conditions I will reef. It's just that I need an effective working sail in extremely low winds, which are very common here.

Deer suggests 7.5cm mast. I could make boom 4cm. Would that suffice? And what about mast taper, should I add it?

 

The skeg doesn't help hold the rudder down. It helps keep you straight while you are rowing, as would a lashed rudder that is part up (so a bit like a kayak rudder)

RW

 

Oh, I misunderstood earlier. I'll think about this. Maybe there is a way to fix the tiller without it going into the cockpit.

 

I have red that book, and didn't find anything on spar strength. Did I miss it?

 

By the way, Richard, in the link you gave me Jim suggests using layered plywood for rudder blade. Actually, this isn't the first time someone suggests that.

However, previously in this discussion folks here discouraged me from using plywood for centerboard and rudder, because 50% of grain are horizontal, therefore, contributing very little to strength. They suggested using solid timber beams glued together and shaped into a NACA foil, with optional fiberglassing.

So why do so many builders on the internet like this Jim Michalak suggest using ply for boards?

P.S. Does anybody know some good, easy to make rudder extension joint? I though about simple rope with a bulky knot acting as a joint, but my intuition tells me such joint will be too loose as far as steering is concerned.

 

There's a whole chapter on spars and rigging (chapter 17, starts on page 163 in my copy).

 

Go laminated strips. Easier to shape, and stronger. Ply is often recommended for beginners as the thinking is "board are flat sheets, and ply is flat sheets, so use ply to make it easy".

If you want a proper foil shape, the cross grain in ply is a mongrel to shape.

 

We're talking the same book, right? "Elements of Yacht Design" by Norman L. Skene? It has 9 chapters, 112 pages in my copy.

 

Eh? Looks like you got shortchanged. I have the eighth edition (fourth printing thereof) and it has 25 chapters and over 300 pages.

 

I probably got the first edition Any chance of... You know... You having that book in digital version?

 

I only have the actual book (pre-digital era). I don't have a scanner at the moment either. Maybe someone else has both book and scanner, and could do the pages about spars.