hollow foam hulls

Spent lots of time today on hulls and beams - holiday here :slight_smile:

Sanded the thin coat of filler on main hull, undercoated and painted. getting ready for servos, winch, etc. Currently weighs about 450 grams(~16 oz). It is very strong - no “oilcan” at all with the foam behind the glass - you cannot flex the sides at all, eventually imprint finger/thumb print. I would go thinner with the foam next time (I cut to 18mm, but would halve that providing I cut accurately - see attachment or my post in Dick’s 60ft video post), and use 4oz cloth all over (I used 6oz on bottom half of hull)
With extruded styrene (insulation blue foam) you could even go thinner!
Compound curved beams (high density blue foam, 6 oz directional carbon vacuumed top and bottom) in “just laminated” state weigh 100 grams each.
The ring bulkheads being denser foam caused a problem when final sanding the whole hull. As long as you are aware that they will tend to become “high spots” when sanding and carefully bring them down to height near the end of the process, they are manageable. I would consider making them 3mm undersize and inseting them into one of the sections next time.
Photos did not work out well at night here with the flash going - later!

That’s some nice work! Would like to see some more photos if it’s not too much trouble.


Did you see the photos inside Dick’s post on the 60’ video?

Otherwise I have more photos following the construction (but not too many photos of the “hollowing time”) that I will post soon.


I really like this construction technique as well. I haven’t had time to work on Ghost train the last few weeks as I have been trying to get a B and C rig built for my IOM, and now I am thinking of building the Ghost Train in this method. I have some questions…

After you cut the hull at the frames and are ready to glue them back, what steps are taken to ensure the hull is straight when re-assembled? Seems like it may go back together all skewed if not on some sort of jig. Do you glue one piece at a time?

Does anybody know a USA foam supplier of 1 lb/cuft expanded polystyrene in 48" x 6 x 6 blocks?

Keep up the pics, they are great.


Mahoo -

I don’t have a supplier - but might do a Google search for lake dock floats. They used to use expanded foam “logs” about 8-10 inches in diameter and about 5-6 feet long under a couple of our docks at my in-law’s lake - but I never did a search for a supplier. Might be hard to find in small quantities, since they probably want to sell you a truck-load.

Try this link - email companies for more info and costs.


Found a supplier in USA. Enough to make 1 main and 2 float hulls

Foam Factory, Inc.
Styrofoam, 1lb EPS Foam
48" x 18" x 6" Thick
$ 56.69 + Shipping Fee: $ 20.00
Total $ 76.69

EPS is supposed to cut beautifully with a hot wire.

Was looking at the Brossard Trimaran and noticed the main hull shape. This hull would be easier to cut with the hot wire as it has flat sides and bottom. I’ll attach a pic here. Also, notice the three rudders. I might do that on mine.


Not to split hairs here mitch - i’ve been very interested in the Brossard Tri and have actually been in contact with the HR person with Team Ocean. The sides appear mostly flat, but slightly concave as seen from the rear. I’ve completed one hull as a mockup/test hull. After playing with the hull in the water i want to make a few adjustments to the design and take a second stab.

Are you planning on going after a design like the brossard?

Not sure. I was originally started a Ghost Train exactly like the plans which is very rounded. But hot wire cutting a styrofoam hull has me thinking flat surfaces are fine on the main hull. It might actually improve tacking to build the underwater section like the Brosard.

Any pics of your first hull shape?


To be honest, i started with a plan from a 2 meter boat i found on dick’s photo page. I’ve scaled it in width 15% and left the height. The thing i failed to realize was that in increasing the width, leaving the height and going from a 2m to a 1m boat, i’ve really begun to distort the original design (the last part i realized only after building.) This weekend though, i was able to actually play with the hull in some water and was amazed by the buoyancy of hull. After placing a 5lb. weight on top of it, i got a better idea of how the boat may sit in the water.

In following the lines of the brossard tri, i want to bring the sides down a bit and smooth out the back of the hull (when viewed from above). I’ll try to get a pic posted of the hull in the near future.

I just tried to post a pdf of the lines but was unable to due to size - 19.5k limit? seriously? I’ll look into another way to get these posted…

Hi guys …

Perhaps this 2 Meter set of lines may be of some assistance in your efforts, and save you some time. As noted, it’s a 2 Meter design, but at least gives a starting point. Boat was in construction when a very good UK friend passed away. Never heard what became of the hulls as he also had a set of floats to go along with the main hull.

If you build and sail it, I think it would be a great way to honor the man who was deeply involved in the BMMA and who was a person who guided me when I first got started. RIP Mike Howell.



Have you the lines for the floats? :slight_smile:


I glued all hollow sections back together in one go. I taped them together with masking tape (one by one) until I had the whole hull/float assembled. Then I checked the centre lines which were still visible top and bottom and the fit from one section to the other. If the centre line was slightly out of alignment I stretched another layer of tape on the high side of the “offending” position.

Another problem comes when glassing the hull/float (mainly the thin floats). It is very easy to stretch/tension the glass fabric layer so there is quite a “banana” in the foam hull/float. Again centre lines are important. If you resin/glass top/bottom at a time you have a SMALL amount of “adjusting” between laminate. Once the other half is cured no further “adjustments” are possible. (my edit here: I recommend top/bottom half over left/right because of slight shrinkage possibilities)

Until I read your post I had not really given a thought to the other axis (vertical) alignment.

Somewhere on the (VERY messy) floor were the offcuts that could be used to keep things in intended shape.


Thanks eveybody for the feedback.

Dick, the triangle shape would be perfect for hot wire cutting using a template for a wire guide. Need something equally simple for floats without being boxy.

Jon, what weight of foam is your foam? Have you found a heavier weight foam can machine to a better finish?

I have also been thinking that you don’t have to section cut the hull at every frame to hot wire cut the inside out. I would think that you would want to leave the bow and stern sections solid, so you could cut somewhere around the rudder post and frame 1 or 2. Then you could cut the section at maximum beam. That would leave two long sections to hollow and less chance of error on re-gluing. Yes, you may not be as efficent removing some foam weight in the middle of the sections, but it would be much simpler. When the sections are apart, you could also use the opportunity to install internals and bracing, etc.

Also, when hot wire cutting the sections a V notch, or saw pattern could be cut by template to help self align the pieces when going back together

Lastly, if the foam is still fairly thick, say 15-20 mm. Would glass cloth even be necessary? I really like a finish of west epoxy and graphite powder to get a strong coating that resembles carbon.



Yes dick, this is the hull shape i started with. I placed it in Illustrator and then drew each of the lines over it on separate layers. I’ve got them drawn in 100% and the stretched-width version (115% of original) if anyone has use for them…

Dick - would you recommend any adjustments to the hull due to the size adjustment (going from 2m to 1m)? in my inexperience i was thinking that a little extra buoyancy from the added width would be beneficial. After cutting it out and setting it on the water, the bow and stern were just off the water surface. Once the rigging, glass, beams, floats, etc. get added, it will sink down a bit - what is the best way to determine the proper water line? Obviously a hull that sits too low in the water is just creating increased drag but what is the best way to add buoyancy - increase in width? Height? These are questions i am pondering…

No - I will post photos when I get home for lunch. You might consider the WATER RESIST floats. If you look at the lines, they could be cut with perhaps 4 passes (top, top side, bottom side, bottom) and then radiused by hand to round things over.

Here are the float lines for this idea.

Mitch - I have experimented with glass epoxy and mixed in some old laser printer toner (black) which gives an “impression” of carbon - but at greatly reduced costs. :lol: Obviously for looks rather than strength. Consider RAKA for glass cloth, as I think you can purchase the really lightweight stuff of about 3/4 oz. x 50 inches wide. It isn’t much good for abrasion, but very fine and not much epoxy to close the weave. Take a look at “pantyhose” material - it is close to having that fine of a weave.

Don’t blame me if you get slapped or arrested for checking the weave. Most women just don’t understand out “technical interests” ! :scared:

Wider hulls will increase static buoyancy and will aid somewhat in sailing buoyancy. Taller hulls will increase buoyancy as hull is forced down by wind. Unfortunately, when hull is depressed, it slows the boat down. I am in the opinion that this may contribute “TO” pitchpole, rather than prevent it. By slowing down, the boat cannot accelerate in gusts, so the top of the mast has a tendency to move forward faster than the hull(s).

Just for the sake of development, here is a new design for the “A” Class World Championships (100 boats entered) built by John Lindahl, a good sailing friend of mine from back in Michigan. Three of his boats are going to the event (Nov 9, 2007) and will be sailed by some pretty competent sailors. As a new design, it will be interesting to see if they are a breakthrough idea. While I conced they use moveable ballast (the skipper) the entire concept is just “wrong” from what we are used to seeing. They look like surfboards set on edge, but the rear underwater sections are almost flat to allow lift and a ride on top of water instead through it. Will have to watch to see how well they perform.

Kind of messes with my mind too.:smiley:

Very interesting idea. I’ll look forward to hearing results…

BTW - where from in michigan?

I’m originally (first 40 years) from Saginaw (east side 2 hrs. north of Detroit) and John lives in Fennville on west side of state up near Holland, Mi.

Here are the other two photos of the 2 Meter that I posted yesterday. Again, I don’t have lines for them, and unfortunately the originals came from Mike Howell who is now deceased.


I will have to measure weight of foam (I bought several - used for insulation - 12’ x 4’ x 6" blocks some years ago of various weights) (weighed at 18oz/ cu ft if my calculations are correct. About “medium density here, with bead size about 1/8”)

I did not cut the hulls at every frame, only at structural points or other sutable points (see pics in Dick’s video 60 footer post - 2 cuts in front of front beam, at beams, and one near rudder post).

Denser foam certianly finishes better, particularly after sanding, and also has smaller voids and fewer tearouts ( from too rough sanding) that absorb less resin.

The more you can put internals etc before glassing, the easier.