Cape George Cutter, righting moments

[CarinaPDX]

Thank you for the correction. Is Todd the one who bought the company from Cecil?

Greg

[Panope]

Originally Posted by CarinaPDX

Thank you for the correction. Is Todd the one who bought the company from Cecil?

Greg

Yes.

He is also the one who acquired the Bristol Channel Cutter and Falmouth Cutter molds.

Steve

[CarinaPDX]

I believe he has done some bulwark replacements, from cedar to something synthetic. Do you know what material he uses for that?

Greg

[Benz]

Originally Posted by Panope

The current owner of Cape George Marine Works is Todd Uecker. Todd is not withholding ANY information. In fact he is helping this effort to the extent possible. The reason he has not provided the righting moment is because he does not have the data. No one does.

I have known Todd as a friend for 25 years and he is now my employer.

Steve

This is the Todd I know....he would spend hours of his time talking to me by phone when I was building my CG31--I've rarely known a more helpful guy.
Long may he boatbuild.

[Panope]

Originally Posted by CarinaPDX

I believe he has done some bulwark replacements, from cedar to something synthetic. Do you know what material he uses for that?

Greg

It is a very high density foam, with several layers of glass, then a traditional teak cap.

For those unfamiliar with these boats, the primary structure of the bulwarks are simply a continuation of the hull topsides. It is the "inner" part of the bulwark that sometimes becomes rotten and needs to be replaced.

Steve

[GRIT]

Thank you Panope, for the clarification. I will let my friend know that the info simply isn't avaliable.

Would he happen to know which spar manufacturer has been used for these boats?

Thanks for your help.
Paul.

[CarinaPDX]

If it was finished by the yard in the '70s or '80s then Cecil and his crew laminated the wooden spars, but AFAIK they were only done on boats Cecil built for himself.. During the same period many aluminum spars came from LeFeil, especially the owner-completed ones, (Missile) In those days that was really an owner decision - remember that these are custom boats - and there was no standard. Perhaps things have changed in the last 30 years.

A clarification on the bulwarks: this is one area that the design evolved. When I got mine started in 1978 the deck beams rested on a glass-enclosed shelf of laminated yellow cedar, a layer of marine plywood was put on top of the beams, then a cedar plank was attached to the inside of the hull to form the bulwark as Steve described, and finally the teak planks were laid down on top of the plywood. Unfortunately the crew at the yard did not do a good job of sealing the small spaces between the cedar and the fiberglass hull, which allowed a small amount of water to eventually settle in there and potentially start rot of the cedar. Because the plywood was glassed at the edge with the bulwarks the water could not usually get further into the structure. I drilled into the cedar every foot and blew out the water and filled with epoxy after drying, and haven't had rot problems in the bulwarks. Anyway, by the early '90s the yard glassed from the top of the hull down, across the plywood and up the house sides continuously to the other side. I remember that the interior face of the bulwarks was glass, laid up on a smooth surface first, but I don't remember what the filler was. I hadn't seen one where the bulwark was cedar then glassed but it makes sense for pre-'90s boats without teak decks. Anyway, using synthetic materials to replace the cedar bulwarks on an older boat like mine may make sense if the cedar gets rot (not yet for me). And in the not-too-distant future the teak decks will be EOL and then a full glass cover (bulwarks, deck, house) will be needed, although probably not on my watch.

Greg

[Don C L]

Just out of curiosity, why does your friend need the righting moment? The original owner of my boat wrote to Olin Stephens for the metacentric height and even he didn't have it since he said they didn't usually calculate it for boats with such deep center of gravity. Looking at the specs of the boat, the length of the mast and the mast weight, it can be calculated. But unless you are planning a change in the length of the mast, why not just refer to the original mast length?

[Adelie]

Originally Posted by Benz

There is a Cape George owner's forum, or was: someone over there will be able to answer the question. There's several home builds.
If she's buying a stick from a mast manufacturer (Selden? Zspars?) they should be able to make recommendations if they know displacement, length, beam, SA etc.
For what it's worth, my Cape George 31 was spec'd for a mast section moment of inertia of just about 5lbs/ft. I'll bet the 36 isn't much bigger...

5lb/ft is not moment of inertia

Moment of inertia has the units kg*m^2 or lbf*ft*s^2.

Area moments of inertia for mast sections have the same units or sometimes area^4 depending on how it’s being used.

[GRIT]

Don.

The present mast is a wooden mast. It's difficult to figure out the equivalent spar in aluminum. If you have a formula to do that, we'd be happy to see it.

Otherwise, the boat's resistance to heel (righting moment) is used to choose an appropriate mast, based on it's strength (moment of inertia).

If the boat was in the water, as mentioned earlier in the thread, we could make reasonable measurements to sort it out. Though the best measurements would be at 90 degrees of heel, we can put weight on one side of the boat, measure it's effect on heel, and extrapolate from that to get an estimate of ultimate righting moment (roughly equal to: "righting arm times displacement"). It's a dead simple calculation on a catamaran, but more complicated on a monohull.

A mast should be able to resist this maximum righting moment, with room to spare. Someone was kind enough to show a formula, earlier in the thread.

And that's why they'd like to have the righting moments of the boat. I'm just the guy who gets to look for answers from those here on Cruiser's forum.

Cheers.
Paul.

[Panope]

Paul,

If it would be of any help, I can likely gain access to the aluminum mast of the Cape George 36, "Millie". She is undergoing a refit in our shop while her mast is being stored at a local rigger's shop.

I could likely take measurements and pictures of the lower end of the mast.

Steve

[GRIT]

Hi Steve.

That's a very kind offer. If you wouldn't mind taking measurements and photos, I'm sure that would help.

Would you mind measuring the mast in: 1. the fore and aft direction (outside to outside), 2. atwartships (outside to outside), and 3. the thickness of the aluminum at the front, 4. and on one side? That should do it, if it's not too much trouble. The total length might come in handy too.

Is there any chance that the rigger is the original supplier of the mast to "Millie"?

I appreciate you doing this Steve. If there's something I can help you with in return, please don't hesitate to let me know.

Thank you, Steve.
Paul.

[Benz]

Originally Posted by Adelie

5lb/ft is not moment of inertia

Moment of inertia has the units kg*m^2 or lbf*ft*s^2.

Area moments of inertia for mast sections have the same units or sometimes area^4 depending on how it’s being used.

You're right. But the moment of inertia calculations boiled down to a section that weighed 5 pounds per linear foot. That gave me a base from which to start shopping.
I admit is was simpler for me since I just needed a round pole for my gaff rig, but still--weight per foot of section is a good starting point.
But now that it's brought up--if the OP converts to a gaff rig (no time like right now), there's no way they can lose the race. More sail area down low, easier handling without halyard winches, less costly to build and maintain. These hulls love a good gaff rig.

[Don C L]

Originally Posted by GRIT

A mast should be able to resist this maximum righting moment, with room to spare. Someone was kind enough to show a formula, earlier in the thread.

And that's why they'd like to have the righting moments of the boat. I'm just the guy who gets to look for answers from those here on Cruiser's forum.

Cheers.
Paul.

Ah, so you are looking for the dimensions of an aluminum mast that can withstand the compression forces associated with that righting moment and displacement?
So this has piqued my interest (again) since I went through something of this with my own boat a while back. Perhaps page 3 of this article has the formula that will help, I am not sure, in finding the P (compression force.) Forgive me if this is too basic and not relevant to the discussion here. I'd love to hear a rigger chime in on this too.

ok, on edit, now I am catching up, now I see why you are seeking the RM30 as PaulS says in post 8.!

[Adelie]

Don beat me to it. Pg 3 of the PDF is a reproduction of Skenes.

Regarding 5lb/ft being an appropriate weight, that depends on the dimensions of the section including wall thickness. If the 5lb/ft is a solid rod then that would be a sucky mast. A solid rod is not a realistic mast and I didn't think you would consider it so but I did take the example to an extreme to make my point.

If the person already has the boat, they don't need to ask about righting moment, they can test their boat to 1* or 5* of heel and extrapolate to 30* using Skene's to determine the starting point for determining the section.

If they want to know what sections other owners already have then there are 3 basic dimensions to obtain:
A. the fore-aft exterior dimension,
B. the transverse exterior dimension,
C. wall thickness.
The last is the only hard one to get. If another owner has internal halyards then you could pop the cover off of an exit to put a micrometer thru.
Yes the actual areas of inertia will mildly affected by the actual shape of the mast, but those 3 dimensions will put you pretty close to what the mast section should be.