Hull reinforcement

Hi:

I built a fiber glass hull (RG-65 compliant dimensions, i.e. 25.5 inches LOA), and I’m in the process of reinforcing it.

My plan is to reinforce the hull with frames (bulkheads?) at about 3 inches from the bow, same distance from the stern, and with two frames holding the keel, at about 1.5 ~ 2 inches from each other, amidships. The keel frames will have holes in them to minimize weight.

I’m planning on using balsa 3mm thick for the frames, and one layer of fiber on each side, with no exposed balsa on them.

Question, as general as the information I gave is, am I going in the right direction?

Marino

The more I practice, the luckier I get.

Sounds like a lot of extra work.

If you use 1/8" plywood instead of balsa, then you won’t need to re-inforce it with Glass.

Keep in mind what your load paths are. The Heeling forces are coming from the mast and shrouds and going into the keel. So you want to construct a brace system that connects the chainplates, mast base and keel box together into a rigid structure. Then the loads will go straight from the mast and sidestays into the keel and you won’t have to rely on the strength of the hull to carry that load. I would think you could do that with one bulkhead at the front of the keel under the chainplates and mast with perhaps a small gussett at the aft end of the keel.

As far as the forward and aft bulkheads, those seem like overkill to me. Unless you hull is really thin, you probably do not heed them. I would re-enforce any area that is going to be taking loads. Right under the jib pivot for example, i might add a re-enforcement to spread the load into the hull (particularly if the deck to hull joint were weak and you didn’t want to carry load through that joint). In the back, I would re-enforce the rudder post and the backstay connection. But again, you are only talking about spreading the load into the hull if your deck is not strong enough to take the load itself.

Hope that helps.

  • Will

Will Gorgen

Great!

Some more info:

Hull is about 3/16" thick.

Beam section has two layer of fiber, 7 inches wide.

Stern has 2 layers of fiber 3 extendin 3 inches forward.

Bow has 3 layers of fiber (I think I over reacted there, I’m not gonna sail in the north atlantic), extending 3 inches aftwards.

Bow and stern are very stiff, so I think I might spare those sections, but the rudder post might need reinforcement.

As far as the deck goes, I’m think of using 1/8" plywood covered with fiber in the top and reinforced with e metal strip and fiber on load areas (chainplates for stays, jib tack , etc). Deck to hull joint will be made with fiber.

Marino

The more I practice, the luckier I get.

You are WAY overbuilt here.
Hull should be less than 1/16 thick…even one metres are this or less. I have owned real boats with thinner hulls than this!!!
1/8th ply is overkill for your deck,you certainly won’t need any extra glass or metal strip on it!!!
If it was mine I would use 1/16th ply for the deck.
Off course this is only my opinion…
Brett

Certainly will keep that in mind next time. Anyway, Our Tartan 30 has a thru hull of almost an inch so I though this was fair…Dumb beginner’s mistake.

Marino

EDIT:

When I stated 3/16 I was GROSSLY wrong (did it from memory). Just measured and is about 1/16 average, little more amidships, bow and stern… Sorry…

Marino

check this site for some info on hull construction.

http://askducksoup.sueandjohnr.com/

click on the Construction link on the right.

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by dansherman

Marino

check this site for some info on hull construction.

http://askducksoup.sueandjohnr.com/

click on the Construction link on the right.
<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

WOA! I’m in the stoneage! [:-banghead]

Of course, those guys are pros… But it seems from the few photos of molds that they preffer a female one, while I made a male mold… Any advantage of the female mold over the male?

Marino

The more I practice, the luckier I get.

If you make a quality female mold, the outer hull surface will be perfect. With a male mold usually the inside of the hull is perfect, and the out side of the hull will need minor finishing work.

It should be noted that it’s cheaper to use a male mold than a female one.

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by dansherman

It should be noted that it’s cheaper to use a male mold than a female one.

<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
And maybe faster as well…

HULL from Female Mold =

  1. Buld male plug and finish smooth
  2. Cover male plug with glass to make female mold
  3. Smooth and polish female mold
  4. Layup glass or carbon to make hull
  5. Depending on mold - remove hull. Maybe have to do some cosmetic finish

While on a HULL from Male Plug =

  1. Buld male plug and finish (sorta) smooth.
  2. Cover male plug with glass or carbon to thickness of hull
  3. Finish, smooth and polish/paint outside of hull
  4. Remove hull from male plug.

here is a link to an interesting way of making a hull using a male mold. I’m not sure how well it works, but it looks cool.

http://members.tripod.com/ghmyc_1m/germanrubber-305.html

Of course when you put the two together, male and female, then you have a compression mold and you get the best of both worlds… finished surface inside and out. Many “light-weight” class boats were made this way in the 70’s as it was before the common availability of extremely lightweight materials. By clamping and squeezing the heck out of it, you would force the excess resin from the mold and produce a very strong material and very thin.

When it comes to costs between male and female, the female are always more expensive.
(this is true with molds as well) :wink:

www.LudwigRCYachts.com

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Larry Ludwig

When it comes to costs between male and female, the female are always more expensive.
(this is true with molds as well) :wink:

www.LudwigRCYachts.com
<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
[:D][:D]

I suppose one could build a "female mold using the opposite shadow templates - but finishing really smooth on the inside of a mold is much harder than finishing a male plug. I tried strip foam building inside a set of female shadow templates, and it worked OK - but when you get to the pointy end, it is almost impossible to sand and polish. I felt I spent as much time “trying” to get a good finish there, than if I would have simply made a male plug to start.

Also would like to add a male plug = hull is best for one-off boats, but if you intend to make more than two, a female mold is the way to go (in my opinion). Finally, one other method I forgot about - but similar to male plug, is to shape foam and glass over - then finish the exterior (fairing and paint) and then decide to “melt” out the foam - or just leave it inside. (a bit heavier). This is a good way to build a quick hull to see how it looks, floats, etc. The weight of the foam is only slightly more (usually) that a complete hull with all the radio , electronics and rig. Thus, if you hand a rudder and keel on a monohull - it should float pretty darn close to final design with all gear but without foam. A good way to experiment with those homemade designs.

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by dansherman

here is a link to an interesting way of making a hull using a male mold. I’m not sure how well it works, but it looks cool.

http://members.tripod.com/ghmyc_1m/germanrubber-305.html

<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

The ?German Rubber? method works pretty well. The plug doesn?t need to bee perfectly smooth or waxed, the inside latex layer smoothens out the plug perfectly even major dents. The outer latex layer makes the hull perfectly smooth and only minor wet sanding was need with mine.
This method is definitely recommended only if you want to make a single (or a couple of hulls at the most) CF or composite hull, and don?t want to invest in a CNC milled mold. The only thing you need is a sturdy plug.
If you want to make more than a single hull (for a club boat to sell) a female plug is definitely recommended, more expensive and complicated to make (the plug) but easier to use and the results will be more uniform.

Gio