New hulls for old beachcat?

Short version, are there any cat designs for sale where the hulls could be used with Hobie 18SX rigging?

Long, drawn out version...

My wife and I sail an older Hobie 18SX on the weekends usually between some local islands within 11nm (22km) of shore. No racing, just island hopping with other Hobie sailing if the weather permits or just blasting around off the beach if a long sail looks questionable. We enjoy this boat, with the possible exception of its weight (way over class weight), but it is starting to show its age. The hulls have been injected with epoxy once already due to delamination and I'll be doing this again soon it seems... I also have to track down some leaks as we are taking on a lot more water then is normal.

This boat has been out of production since 2003 but there are lots of spare parts available as well as used boats on the market. The last few boats I checked out also had soft hulls so didn't make the cut for spare parts boats.

In the past I have toyed with the idea of building a lighter cat such as the Blade F16 due to being a cat that’s at least as fast as our 18SX (probably faster), 25% lighter (don't need as many people to help move it on the beach), carries its buoyancy low (reduced tendency to pitch pole was one of the reasons we chose the 18 over a Hobie 16), but couldn't justify the cost of a modern racing rig just to fun sail. I've often seen it mentioned that building the hulls for a project like this is the least expensive part with the rig, sails, foils, etc. usually costing much more.

So the question is would it be feasible to build new hulls (preferably out of ply) as a winter project and use most of the parts of the old Hobie, with the possible exception of the dagger boards since the trunks are usually part of the hull design?



Specifications
Length 18'
Beam 8'
Min. Class Weight 400 lbs.
Draft (Boards Down) 2'6'
Mast Length 29'6.5'
Total Sail Area 240 sq. ft.
Maximum SX Wing Load 550 lbs.
Hull Construction Fiberglass/Foam Sandwich




(Typical boat, not mine)

 

Short answer: Yes you can!
Long answer: But not out of plywood. It would be heavier than your old Hobie.

 

Great! Could you share the names of any designs that might lend itself to this use?

Why is that? I was under the (false?) impression that tortured ply/epoxy was a stiff and light construction method for one off boats, as used in home built Tornado and Blade f-16 cats.

 

I've heard of builders that used the old hull as a mold for strip planking. You wouldn't be able to staple into the hull but you could use rubber innertube strips wrapped around the hull to hold the planks in place. You could use short staples to bridge between Planks.
Your new hulls would be as light as an original Hobie and a whole lot more elegant.

 

new hulls

You could build tensioned ply or 6 mm strip plank paulownia/cedar/planked balsa/strip foam and glass, way lighter than your original hulls, in fact the comparison is such that there is no comparison. I would suggest, if you want to retain the Hobie hull shapes, to make female frame moulds off your originals - and there you go mate.

 

Thanks for the input guys!

Considering that the original design was done in 1976 I would imagine some of the newer designs would offer improvements. I would want the best return on the time spent building so would go for whatever design would make the best use of the original rig. I would also feel more comfortable following well laid out plans of a proven design and only changing the beam mounting then starting from scratch and hoping my own internal hull structure would carry the loads.

 

You could try this 18'surfcat. called a Chaser in ply from http://www.pelinplans.co.nz/catalogue.htm

All up weight 250 lbs. 6 sheets of 4mm ply, a sheet of foam, a little timber and some glass in the hulls. PM me an email addy if you want and I'll send you a scan of the catalogue page which includes a materials list. Would go well with your larger rig.