Efficient cats

Questions and Answers about the Woods Designs, multihulls and others.
SalmonMan
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Re: Efficient cats

Post by SalmonMan » Wed May 11, 2016 1:43 am

I am also still very interested in the Jazz 30. I'd like to see a rendering or a drawing or two. Plus a description or scope of the boat. A study plan would be excellent! Difficult to purchase plans without much information. The closer it is to the Sliver 29 made by SuperCat of South Africa the more likely I would be to purchase the plans. The study plans would help myself and others to make an informed decision.

Thank you!



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Re: Efficient cats

Post by TomTom » Wed May 11, 2016 1:56 am

Richard - Thanks for the reply - I remember somewhere it was mentioned that the hulls for the Jazz 30 were too narrow to be used for accommodations or anything useful?

Is this the case - or can they still be used for storage, a head, shower etc?

Are you saying that if the SK 32 is built too light it will actually be less efficient than if it is heavy?

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Re: Efficient cats

Post by Woods Designs » Sat May 14, 2016 5:52 am

To Salmon man - email me direct on woodsdesigns@gmail.com and I'll send you some information. Jacques and I are currently still discussing the options for the larger Skootas and Jazz so that will be the quickest way to get the information you need.

to Tomtom, I emailed you direct with a bulkhead drawing.

Sorry for the confusion. All boats, power/sail, 1-3 hulls are designed for a specific displacement. Anything more or less decreases the efficiency of the hull. So for example if you built a Skoota 32 without the cabin interior it might weigh 1000kgs lighter. So knowing that, I would draw finer hulls, each with .5cu m less displacement that are thus faster. In practice using the existing hull might mean it floats so high the props are not sufficiently immersed, and the forefoot slams as it is also not immersed. But I haven't seen the need to do the calculations so cannot be sure

I am seeing the Skoota 32 again on Wednesday so will post more photos later in the week

I hope that helps

Richard Woods

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wej
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Re: Efficient cats

Post by wej » Mon Jun 06, 2016 12:02 am

Ever post the other pics?

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Re: Efficient cats

Post by Woods Designs » Mon Jun 06, 2016 1:36 am

I only got some pictures emailed to me today. I will post them tomorrow, but the first two hull halves have now been made. Its all looking good and very light

Richard Woods

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Re: Efficient cats

Post by Woods Designs » Mon Jun 06, 2016 2:09 pm

Ian Critchmoor has been busy building the first Skoota 32. He is making the hulls in two halves in a temporary mould, I posted photos of the basic mould a couple of weeks ago. The boat is built in infused foam sandwich.

The photos here show the glass cut for the inner hull side (note the cut out for the bridgedeck), the infusing vacuum bag and finally the first hull coming out of the shed. Note the hull halves will be joined with both an inside and outside glass joint, hence the minimal gelcoat along the keel line.

http://imageshack.com/i/pms3PYGkj

http://imageshack.com/i/pnHQJOTpj

http://imageshack.com/i/pllDeTeuj

The outer starboard hull and inner port hull halves have now been made. The next job will be to remove the temporary hull sides and reverse the frames to make a new mirror image set of mouldings. Then the hulls can be joined

The weight for one complete hull will be 220kgs excluding the joining.

Infusion and vacuum bagging sound daunting but any good laminator can do it easily enough. Home builders don't need to use either technique though. Instead you can use scored "contour" foam and regular glass and a wet layup. That is how I have always built my own foam sandwich boats and if I was building my own Skoota 32 it is what I would do.

The temporary mould takes a bit of time to make using melamine faced MDF (the stuff kitchen worktops are made from) but its cheap to do. And there is no filling/sanding/painting as you get a gel coat finish. So in the end you have a more valuable boat built quicker than any other method.

You can see more on the Skoota 32 here http://sailingcatamarans.com/index.php/ ... -skoota-32

Richard Woods of Woods Designs

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Re: Efficient cats

Post by TomTom » Tue Jun 07, 2016 4:46 pm

Richard - am I right in assuming that this technique is better suited to your hulls that have symmetrical hulls as you only need to make one mold and you can get two hulls out of it?

Or would this technique still be worth considering on a Jazz 30 build with asymmetric hulls?

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Re: Efficient cats

Post by Woods Designs » Tue Jun 07, 2016 6:06 pm

you are right, if you have an asymmetric hull you would need two temporary moulds. But even then I would think it would be quicker to do that than build from flat panels and join them, and ultimately cheaper, especially if you were paying "first world" labour and rent prices. In your case only you can decide.

Richard Woods

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Re: Efficient cats

Post by TomTom » Wed Jun 08, 2016 3:25 am

Trying to get my head around how you would do this...but the idea of not having to fair something that big is quite appealing ... something along these lines?

1) make a "basket mold" - something like this - http://bateau2.com/howto/basket_mold.php
2) use the melamine faced boards with the melamine on the inside
3) mould release wax
4) gel coat
5) fiberglasss
6) insert the plywood frames and tape them in?

Am on I the right lines?

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Re: Efficient cats

Post by jacquesmm » Wed Jun 08, 2016 10:27 am

You still have to fair the seams but yes, that is the sequence I use when building a small foam boat with the exception of gel coat because I prefer epoxy as the resin.
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