Hull thickness

Ryan · Post by **Ryan** » Sat Feb 11, 2006 7:18 am

What is the thinnest hull that you all have seen in your boat building/restoration travels? I am restoring a Hughes 25 and I have been surprised at how thin the actual hull lay-up is in all the places I have had the opportunity to measure it. The old thru hulls were in a part of the hull that measured on the short side of 1/4", and this seems to be fairly consistent. This is going to be an inland lake sailboat, so it won't have to deal with strong wave action, etc, but I was shocked to see how thin the hull actually was. It certainly doesn't have the 3/4" + sections of glass like I have seen people on here have to contend with.

Tony · Post by **Tony** » Sat Feb 11, 2006 4:21 pm

Our last boat, a Harstad 31, had a thin layup. In the thickest part of the hull it was only a bit under 1/2 inch. The topsides were in the 1/4 inch size.

JetStream · Post by **JetStream** » Sat Feb 11, 2006 8:05 pm

You can read about the thin hull thickness on my 1961 38' Javelin on my website http://www.javelin38.com. I talked with Dave Gerr, the marine architect, about it and according to his books, 1/4" is fine for a boat with a 25' waterline length. Apparently the scantlings are more rated for waterline length than overall length. I think the material is plenty strong for your length but might leave a little stiffness to be desired. I plan to stiffen the Javelin with athwartship ribs in places that I would prefer a little less oilcanning of the hull.

It has been a mystery to me as to where the Hughes molds came from. I saw a picture of a Hughes 38 that looked very similar to the Javelin hull form.

catamount · Post by **catamount** » Sat Feb 11, 2006 8:16 pm

I think the Hughes 38 was an S&S design. Also it is the same hull as the Hinckley 38. In fact, I heard that Hughes actually built the hulls for Hinckley.

Back to the queston of hull thickess, I'm sure that my San Juan 21's hull is not more than 1/4" if that. The same for my Laser, and our fiberglass tender's hull is probably only 1/8"

Regards,

Ryan · Post by **Ryan** » Sat Feb 11, 2006 9:15 pm

Hughes information is hard to come by, even with the internet. I know that Hughes and Columbia were in cahoots with the 25'-26' length boats, but I believe that was in the seventies.
The LWL for the Hughes 25 is only 19', so I'm feeling a bit better about the lay-up thickness. This boat turned into a gut job, and there was very little in the way of stiffening members, or even real bulkheads. That will change with the rebuild, if for no other reason than to give me a little peace of mind and prevent the oil canning mentioned above.

Post by **Tim** » Sun Feb 12, 2006 7:50 am

1/4" of laminate is plenty of strength for a 25-footer of that type; it's just not very stiff over longer unsupported spans. Fiberglass is very strong; one doesn't need a lot of thickness to acheive a very strong piece, but since fiberglass is very flexible, it is common to reduce the span between structural members to stiffen the overall structure; in addition, thicker laminates also help counteract this tendancy.

Some flexing is fine (all boats do), but if it is excessive, the laminate will start to break down over time; too many flexes will break anything, of course. The number of cycles is in the millions.

All you need to do is add some lightweight (small) internal stiffeners to help counteract any tendancy of your 1/4" thick hull from flexing. It doesn't need to be big, beefy structure, other than 2 or 3 main bulkheads. You probably don't even need to install much, but if you want to reduce the flexing (oilcanning), if only to make yourself feel better, then some thin strips of foam or wood glassed in place will make a strong internal structure that will stiffen the hull appreciably in those widest unsupported areas.

In short: add as much structure as you want, but adding too much weight will seriously affect the way your boat performs and sits in the water, so be careful of going overkill. For your simple inland water needs, you don't need to go too crazy.

I promise you there are hundreds of Hunters, Bayliners, and other cheesy boats out there--many that are larger than yours--with hulls no greater than 1/4" thick. They even manage to stay afloat.