Affect of tub width on handling

[PaulHail]

I think I have a grasp of the effects of sponson and ski ride surface widths, angle of attack and sponson width in regards to how a boat handles.

I've been sketching and pondering ideas of laid up composite tubs and such a design isn't restricted to the typical streamlined 2X4 shape of a built up wood tub. The question I have is for oval racing how much of an affect does tub width have on the hulls handling, and how much of it is driven by the space required for the fuel tank? It seems that aside from the area required for the fuel tank, tubs could be narrower if the width wasn't needed for flotation when the hull is at rest, or for hydrodynamic stability. Saw boats are often narrower than oval racing tubs, why can't an oval tub be narrowed up to save weight and potentially gain speed.

 

[gil sonsino]

Paul I've been applying narrower tubs and sponsons on my fiber Fe riggers with great results of speed and handling......I see no problems with nitro or gas one's once you have enough fuel to finish a heat.With wood boats I think narrower tubs would flex more so it's important to minimize too much torcions improving all the structure of the tub .Gill

Gill

 

[Amp Eater]

I have scratch built some skinny mini's over the years and have one ready to field test when the

weather allows. I would think a wide tub will react to rough water faster than a narrow one.

Here is the design narrow where I can get away with it and long lanky for stability but helps flotation.

Will post a vid when able. Weight savings was the goal by not using typical hardware bolted to

the transom of course in this case not much transom anyways.

 

[PaulHail]

Gill,

Thanks for the feedback. On your carbon fiber riggers, how many layers of 200 gsm cloth do you use for the tub? And do you use any core materials on the sides of the tub or other areas of the tub? My thought is to make a multi piece male plug, layup the carbon and vacuum bag as one piece over the plug and then hopefully pull the plug out and then cut in hatches and add bulkheads.

Bradley,

I've followed your mini outrigger designs and they motivated me to get a pair of Picco P-zeros, hardware, props and wire drive units. It seems the toughest part to find for the P-zero is a header, though I got a couple of headers I'm going to try and adapt. I'm also working on a few designs for carbon fiber pipes but need to get some high temp resin.

 

[Terry Keeley]

I built a couple tubs in '99 by bagging 2 layers of CF sleeve over a Kledgecell plug:

http://www.sollercomposites.com/composites/carbon%20fiber%20sleeves.html

Put the bulkheads & transom in the plug, covered it with two layers of sleeve and bagged. Cut open the hatches and chipped out the foam.

I've also done some carbon over Rhoacell tubs: https://www.intlwaters.com/gallery/thumbnails.php?album=707

The tubs I built in '99 are going into they're 19th season!

 

[PaulHail]

Terry,

I'd hadn't seen the pictures of your build. Awesome boat and a very well documented build. I'm going to have to go through the pics and comments in depth. I'd never thought about using a router with a guide bearing against a template to cutout parts, huge time saver!

From the research I've done, it looks like you need ~1000 gsm of cloth to get a 1mm thick laminate, which would require 4 layers of carbon sock. I know carbon can be thinner than plywood but I don't have the experience to know how much thinner I can go. I'm thinking of using 3mm Soric core mat for the bottom and sides of the tub. It seems like a prudent minimum would be 1 layer of sock against the tub, 2mm soric and 2 layers of sock on the outside of the tub. I'm also thinking perhaps using a strip of tow along the sides of the tub for additional stiffness. For the engine mounts I'd use 2mm 6061 inserts on the sides of the tub replacing a section of the Soric.

I like your milled maple boom supports, nicely executed.

 

[Amp Eater]

I use Profi .8cc tuned pipes these folks may sell them seperately:

http://technohobby.com.ua/online-shop/en/engine-profi-08cc-12-f2

This guy gets them and sells on ebay can message for when the next order may happen:

http://www.ebay.com/usr/speeddomingoe?_trksid=p2060353.m2749.l2754

Sportwerk Manifold pipes are a perfect fit for the Picco .8cc engine.

Just have to cut off a portion of the pipe.

https://shop.stormerhobbies.com/product-p/SWK4122.htm

 

[Terry Keeley]

From my experience that 200 gsm cloth (6 oz/yd2 over here) ends up about 0.008" per layer when bagged, so you're bang on that 5 layers would equal about a 1 mm laminate. IIRC I used 2 x 4" diameter sleeves of the 12K 15 oz/yd2 material and ended up around the 1mm thickness. They've held up well.

Had to look up that core material, which one are you going to use? http://lantor.com/lantor-soric/

I made some sides for a buddy's 3.5cc boat with 2 layers/side of 3.8 oz cloth (1K 24 x 24) and 1/8" Rhoacell 71 and molded the top/bottom out of 2 layers of the same cloth, came out nice. Very light and strong.

What size boat(s) are you building?

 

[PaulHail]

Terry, the sleeves I've been looking at are ~250 gsm, so looks like I'd need four sleeves to get a 1mm laminate. I'm looking at the Soric SF as that's what my supplier carries. I need to get some resin and fiberglass to fix my full size boat so figured while I'm at it, order some extra resin, core material and some carbon cloth.

I'd first planned on building a JAE 21 and 90 from wood, but am now leaning towards making up plugs at least for the tubs and I'm not sure if I'll go with the conventional wood over foam outriggers are make those composite as well. I'll be building a 45 in the future and possibly a 67.

 

[gil sonsino]

Terry is correct I use 5 lawyers of cf cloth and cf fiber tape (3 lawyers) to join parts.On the motor section I also like to glue a piece of cf sheet of 2,5mm as a reinforcement for the motor mount.Bulkheads are made from 2mm c.f sheet i fabricate using vacum bagging.BTW no gelcoat on my fiber boats at all.Depending on the amount of buildings I like to make bulkheads using Coremat .Something important to me is also know the exact time I have to cut all excesses in the mold before the final set of the epoxy resin otherwise it is a pain in the neck have to trim such a hard material.Terry's boats are very nice and clean too.Gill