Couldnt I just add foam in the leeward hull and remove all doubt?

class min's would be the target, no?

Are you asking if I think it could be done? On an F18, it would be easy.

On an Acat I think it could be done, but I dont have any data to support that position. Wouter did his F16 in ply, so he might be willing to share his thoughts.

Bill

Bill,

I was not on the offensive, just wondering if you knew what the hulls would weight if done in ply or strip. The F-18 would be easy, agree. The F-16 is not as easy, but I see the A-cat as difficult to get down to min weight. Even without the need to take bridle and spi loads.
Ply or cold moulding would probably be better than strip as you dont need to add glass. It could be the ultimate wooden boatbuilder challenge. Build a set of competitive A-cat hulls with as little carbon and as much wood as possible.

Did not the min. weight use to be 90kgs, before it was lowered to 75kgs? There used to be quite a lot of wooden a-cats earlier (Unicorn comes to mind), didn't it?

The ply F16's can be build down to minimum weight as their hulls (combo of 3 mm and 4 mm ply) are respectively; Taipan F16 23.5 kg/hull, Blade F16 25.5 kg/hull. These will be competive BUT the newer glass laminate boat can arrive at the same minimum weight while being less strickt on the overall weight of the other components. In effect the laminate hulls are now being build lighter then the ply hulls, which is an achievement as it took Boyer about 10 years to make the glass Taipan hull as light as the ply ones. These F16 ply hulls does include a number of ply bulkheads and foam bulkheads (floatation). By luck, 4 mm ply is just right for the F16 hulls, so not much weight is lost there because of the standardized thicknesses of sheet ply.

But you have to work with alot of attention to details and weight, it takes effort to get this low.

The ply A-cats I know of used 3 mm ply over the whole hull and skimmed on the bulkheads. If I remember correctly these A's had only a bulkhead at the bridle, mainbeam, rearbeam and daggerboard well.

I estimate that these A-cat hulls couldn't be lighter then 16 kg per hull, probably they were slightly heavier in general, I guess just below 20 kg.

I did hear however that the bows would break-off if you put the boat into a pitchpole. Roughly speaking these lightweight ply A-cat hulls did get down so low by sacrifizing strength.

On my boat I rather not stand on the 3 mm thick parts. The difference between a 4 mm wall and 3 mm wall is noticeable. Luckily the section between the beams (and a little beyond) is 4 mm on the F16's. I have thrown this boat about pretty good and no failure as of yet (3 seasons and counting), so my hulls are strong enough.


On F16's between 50 and 60 kg is invested into parts other then the ply hulls (when not using carbon). Bill, how much is used in this respect on the A-cat ?

But again I seriously doubt if any ply A-cat building plan is producing a competitive hull anymore. The last ply plans were made early 90's I think (about mark 3 boyer A-cats) and would be very comparable to the Taipan hull shape but less tall, longer and less crossectional volume.

I hope this helps

Wouter

Who said you could move the crew around? <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" /> They stay put when the rig is moved. How they actually get there with the sail in the way is not part of the theoretical argument. (If you change more than one variable, then it's impossible to discuss the effect of just moving the rig. Start with the crew in the middle if you like - the net effect will be the same).

Righting moment is a torque. The total bouyancy and total weight forces are always equal. What changes is the moment arm. It makes no sense to talk about just bouyancy providing righting moment.

Capsize moment is also a torque (sail pressure one way up high, dagger pressure the other way down low).

The way to look at this is one torque countering the other torque. It makes little difference whether the force from the sail is left or right of the combined CG.

Force diagrams of the sort I provided are a standard way of showing these things. English sometimes falls short.

Rolf,
I didnt take your question as being on the offensive, I just wasnt clear what you were asking.

Wouter,

My foam/carbon/epoxy hulls with no bulkheads or transoms came it at 6kg per half, right out of the mold and 33kg for the whole platform, no paint no tramp. I didnt document the hull weight pre "beamed-up"

The XJ Acat hulls are between 18.2 and 18.9kgs (3 boat sample)per hull.

So if you could build a set of Acat ply hulls for under 19kg you'd be in the right ballpark and could get in under 75kg if you were careful about everything else.

Bill

Ok, 19kgs as max pr hull. Do you know the surface area for your hull?

The surface area of an A2 is 5.9m2

Gareth

Bvining,
You can build ply A class's at min weight from ply.
I know 3 guys who did it in around 1989 with alunimium masts.
I'm told when weighed they were 74kgs rigged.
I believe this to be a legit weight because they sailed in the worlds either that year of the following and they had to be weighed.

Now this is an older style of hull which has more surface area too.
You have to be good, very good, but it can be done.

BTW:- In recent years I've seen two of them still sailing.
Don't know where the third is but I think it was sold overseas.

Regards,
Phill