Figuring out new nail plan and spars

[pandelume]

This is my first post and my first boat, and I could use some of the expertise of those with a little more experience (i.e. you people). Here's the deal:

I have a modified copy of the Edson I. Schock design "Sharon Potts" (http://www.dngoodchild.com/divide_for_sail_boats.htm). The modifications consist of a new compartment of about 1.5 ft length added to the stern, and a short snub-nosed bowsprit projecting maybe 10" past the stem.

I'm working on fixing her up, and I've decided to put together a new rig if it seems feasible. I don't have a particularly good reason for this, except that I'd like to have a somewhat shorter maximum spar length, and that I don't care that much for the existing rig, pictured below.



It has a main of 100sq. ft and a jib of 30 sq. ft.

I'd like to change the rig so something like the one shown below:



In drawing it, I have kept the geometric center of sail area for the two in pretty much the same position fore and aft, although the new one has the center lower. In the second picture, you can see the approximate size of the extension at the stern. I would replace the very short bowsprit with a longer one, possibly reefing.

Any thoughts on this? I'm new at sail design, so maybe I'm being foolhardy, but I like the new plan much more than I like the old. I figured I could do some polytarp sails, and if it doesn't work out I'll have lost little but time.

Second, to make the new bowsprit and boom, I have secured a 25' cedar pole, maybe 5.5" diameter at the foot and tapering to maybe 2" at the tip. This had been dried, peeled, and varnished some time in the past, but the varnish has largely worn off. I actually have two of these - one to make a new mast - but I found a secondhand spruce mast that seems like it will suit admirably. Any advice on making spars from these? I'm not sure what dimensions to aim for - for example, how much longer than the foot of the sail should the boom be? Would 3"maximum diameter be suitable for the bowsprit? Perhaps cedar is a poor choice, although the cost for these poles makes it very attractive. I don't imagine there are definitive answers, so any input would be welcome.

[pandelume]

Pardon me, the title should read "sail" not "nail".

[Woxbox]

I'd say if you're in the mood for experimenting, just go ahead and do it. The spar sizes you cite should be more than adequate, and if the center of sail area is the same, you should be ok.

Just understand that sail rigs are made tall in part because they work more efficiently that way. You'll have the same sail area, but a boat that won't sail quite so well, especially into the wind.

Also, I assume you understand that poly tarps can't easiliy be made to take on the shape you really want, which will cut the efficiency a step more -- although there are others on this forum who can explain in great detail how to get a decent sail out of the stuff.

Finally, if you've sailed a boat with a boom that long, you'll know that it can get stuck in the water and cause some trouble. Angling the mast aft helps correct for this -- it makes the sail and boom swing up as they go out.

Some like to do all their figuring on paper and then build it right once. If you prefer to do your development work out on the water, as I do, then put it together in a solid but temporary sort of way, take her out and play with the setup until you get it right. It's the best way to learn.

[boatbear]

Welcome to the forum. I’m no expert but have built a couple of boats and designed and made sails that work, and all the spars and bits and pieces that go with it.

Firstly, why are you adding the compartment at the stern? It would be a difficult thing to make fair. I suspect that it may always look like a lumpy addition – still, anything is possible. Don’t let me stop you; I’m just intrigued.

Nextly, your proposed sail plan has some little difficulties (to my mind). Getting the centre of effort down low is good, however the long boom means that going downwind can be a rolling affair. My 6m (18’) dory has a longish boom and there are times when I have to tack downwind, fighting the tiller all the way trying to keep the boom out of the water. In gentle winds it is just fine. Also, reefing can be a problem if you can’t easily reach the end of the boom.

I can’t help with the cedar mast question except to say that if it is strong and light you are well on the way. Looking at other boats of similar size will give some clues on spar diameters etc. I’m sure others with a lot more experience will help here. My mast is spruce (I think) and I made it hollow and elliptical, 85mm x 65mm (3.5” x 2.5”) at its widest and tapering to about 50mm (2”) at the top. It has stays and is about 6m (18’) long. The boom is about 4m (13’) long, 65mm diam (2.5”), gaff just a bit smaller, and bowsprit 50mm (2”) diam. All have proved strong enough so far, and are very light.

I wish you well with your project and look forward to progress reports. I see that Woxbox has posted some good advice while I have been writing this.
Charlie

[pandelume]

Thanks for the advice, you two. Boatbear, I'm not adding onto the stern, I got the boat that way - and luckily enough, it doesn't seem to stick out more than any of the other unfair (not fair?) spots:




Close up it looks like this:


I'm not sure why the previous guy added the compartment, unless it was to add the small motor well visible on the upper right. Maybe he wanted additional storage?

As an update, I'll add that I just came in from sanding the deck, and right up at the front, next to the tiny bowsprit, I discovered a patch of rot soft enough to push a screwdriver through. The deck is 1/4" plywood, and this is right near the edge where an anchor fairlead or something was poorly bedded. It's not a large area, so hopefully it won't be too hard to patch - anyone have experience with this?

On the subject of rot, I also discovered that several of the frames (1"x2" pine or other soft wood) are cracked or rotten - probably due to standing water left in the cockpit. Only the part of the frames that supports the bottom of the hull seem to be in bad shape - the sides seem fine. The bottom planking (plywood) also seems to be OK, although a bit worse for wear, but there is a slight bow from where it has been sitting on the trailer. Perhaps the bow is due to lack of support from the compromised frames?

Anyhow, this is upsetting, but it doesn't seem too discouraging...yet. Any advice on how I should go about replacing the frames? Just bed them down in thickened epoxy after sanding down the planking?