Hull supports

Greetings to all

This question is basicly for those that are building hulls. Mainly IOM style sailboats.Also the boat I am building will not be used in races outside of our local pond.

After hull has been planked and fiberglassed, are you putting hull supports in?
I recently finished the hull for a triple crown (my first scratch built boat)and am thinking that after the fiberglass is placed the hull may still require additional support seems very flimsy right now and unsure if the fiberglass will add the additional support. I have built Kayaks before and we placed ribbing inside the hull for the same reason. On the kayaks there was frames then a rib or two then the next frame. The ribs mainly supported the hull shape as the \frames did just not as heavy. I used 1/8 x 1/2 steamed wood strips. From all the pictures I have seen of R/C boats under constrution there does not seem to be any ribs added. Nor is there any frames, only deck supports.

Am I just concerned over nothing?


And the question would be…???

Oh, I get it. It is like the game shows where you get the answer and have to come up with the question.

I am going to take “Building an IOM” for
$1000.00 Bob

EDIT: Looks like the entire post is there now.

Peter R.


People are not putting hull supports in planked or molded hulls.

HAHAHAHA was hoping no one would see my screw up before I got the question into the message

You are just to fast



You probably do not need to stiffen the skin with any frames or stringers.

What are you planning on doing for the deck? If you are going to have a fairly substantial deck, then that will stiffen the boat quite a bit. The typical IOM deck (even with the large cutouts) will turn the hull structure into a Monocoque structure that will make it quite stiff.

There are a few areas where extra stiffness is needed. I would plan to include a bulkhead that connects the mast base, keel and chainplates. You want to integrate this area together so that the heeling loads of the sail are transmitted directly into the keel strut. You do not want the hull skin structure to carry much of this load as it is really not strong enough to do this. Try to integrate your sail servo and rudder servo into the keel structure as well rather than the skin of the hull the keel structure is better at handling those loads. You will probably also want to re-inforce the area there the rudder post is installed (unless the rudder post sticks through the deck - then you should be fine).

The other area where people add re-inforcement is in the deck. Make sure your jib pivot is well supported as there is a decent amount of load pulling up on the deck in that location. You will also want to pay attention to how the sheet loads are carried. If the deck is free to flex due to the sheet tension loading, then you may want to re-inforce the deck in those areas.

Hope that answers your question…

  • Will

Will Gorgen

are you glassing the inside of the hull? what weight glass are you using if you have and is it still not strong enough? the loads on an rc yacht are a lot less than on a kayak and does not have to be any where near as strong a little bit of flex in the hull is a about right

When the Apprentice knows more than the Mentor its time to quit!

A related question. If a person did make a hull that would “oil can” how would you know? Imagine that if when a largeish wave hit the boat, the hull would pop in and then pop out. What would the boat do that would make you relize what had happened?

Vancouver Island


One thing I can assure you. As long as no one intends to sail through your boat, you can make your boat almost as thick as a piece of paper. But I really recommend you to offer a little weight for some strength. Just take a look at my IOM after she met another one:
It is reparable, but still not nice.


It was the running joke for a long time back in the old days about the “hull of the month class” otherwise known as Marbleheads when they were at their peak, that the guys that were using MONOKOTE for their deck would tighten up the back stay and snap the hull in two.

You can insert some clever pieces of glass at any time (as long as you can access the spot)that will give it tremendous strength.
Common sense tells you where the most stress is applied to the hull (mast, rudder, keel) and those areas are going to be the first to fail if your structural integrity is compromised.

Flex in the skin of the hull under pressure from your hand is not a concern as water will apply it’s force more equally, but your high stress areas must be strong enough. You will know as soon as you handle the hull.