All posts by Kurt

Composite Chainplates

Carbon chainplates sound good for marketing, but E-glass is just as good. Here is why. Imagine a 30 trimaran that weighs say 2000 lbs. The chain plate vertical load at overturning will be about 1000 lbs. Add in vector of shroud angle and crew and lets say a static plate load of 2000 lbs.
Hand layup and vacuum bagged carbon uni should have a tensile strength of some 80,000 to 120,000 psi depending. That means a chainplate of 1/35″ or 0.7mm. Now, tensile is not the only load, but for now assume it governs. Double it for grins and put one at each end of a rod or something. Even at 1/15″ (1.6mm) it looks way too weak to most of us. Most of us do not have an instinctive feel for how much carbon looks right. Most of us would only be comfortable if the thicknesses look to be at least what Skenes would require in stainless. That gives dozens of safety factors just to get it to look right.
E-glass uni will not be that much less tensile strength than the carbon uni. Expect maybe 60,000 to 70,000 psi tensile strength. So even with e-glass you will still have a safety factor of dozens.   Carbon fiber does have better than twice the fatigue resistance, but the safety factors are so many, it doesn’t matter.
E-glass does provide better shock absorbing, theoretically. Its stretch to failure of around 6%, combined with the same from the resin, should help absorb shock. The only problem is that with a safety factor of 20 or so, the e-glass won’t give anyway. Its not loaded enough to give.

Carbon fiber is fun for this job, but not at all necessary.  I know, its heresy.

this is a hound actually, but the same idea as composite plate

PostApocalyptic Boat Building Update

I am working on an update to my article first published Spring of ’09? First, I can’t believe there is still a recession. I will be adding a few new cores and links.
The best part about it was I got a call from Meade Gougeon in the summer of ’09 about the article. He thought is was the best thing he had read in years and it motivated him to get back into the building part again, as he told me. We talked at length about it at IBEX in ’09.
Back in ’08 I submitted the article to Professional Boatbuilder. They told me that they were not interested in it.  It seems that they don’t count owner-builders in their readers. I’m guessing I have close to 2000 builders over the years. I’m also guessing almost all of them read Pro Boat. Thats not nothing.
I imagine my comparing product brands was the problem. I should have known that.  The advertisers would not like it.
The odd thing was that Pro Boat published a fine exortation to boatbuilders by Bob Lacovara in Feb/Mar 2010 called…PostApocalyptic Boat Building.  They had my article there for months before that. How did that work? Oh well. Kind of low though.

Rowing Record

I just learned that two teams, each with a KHSD hull design, have set out to break the rowing record across the Atlantic. One is a catamaran and the other is a trimaran but both use the KHSD Formula 40 catamaran hull design. They are Team Hallin http://www.hallinmarine.com/team-hallin_2.htm and Big Blue http://www.rocexpedition.com/index.html. Team Hallin left Tenerife on Jan. 6th and is reported on track to set a new record. Blue left on Jan. 11.

team Hallin

Marine Engine Beds and Structure Bourne Noise

Some 15 years ago I attended a lecture by acoustic expert Joseph Smullin on structure bourne noise and how to attenuate it. Our light multihulls are particularly vulnerable to that. Off top of my head, this is what I remember.
As I recall, the features needed to attenuate the noise include, more core weight, more laminate elasticity, add cross structure in the direction of engine rotation, and isolation of the engine and beds from the hull.
I revised my engine bed drawings to take advantage of that then new information. To best of my knowledge, none of my builders until now has ever followed my plans. It doesn’t seem to matter if the builders are highly regarded like Schooner Creek or the inept like Shaw, they slam in a pair of wood 4 x 4s and call it done.
Use minimum 100 kg foam. Use the more elastic type foam. The cross bracing is critical to reducing the noise. Joe preferred the engine beds not to sit directly on the hull, but on a layer of elastic like trevera. I expect that hull bonding adhesive would work as well. This engine bed from the Arteran Catamaran builders in Estonia look great.  OK, I’d like to see a bit more cross connection, but these are the best so far.

motor mount for the Arteran powercat

Edge Seal Roundup

There are many ways to seal the edges of a vacuum bag. A survey:
SEALANT TAPE AT200Y YELLOW from Fiberlay works very well, but is one-time only. I could never get it off the bag so the bag was damaged getting the part out.
PVC pipe snap bead. I recall seeing this in the Gougeon’s magazine. A pvc pipe is ripped and then snapped over another, with the bag plastic in between. I resisted that way as the ripping is one more job to do.
Storm Window Bead. I prefer the inexpensive storm window sealer (Frost King by Thermwell Products http://beatlas.com)1-800-299-5700.  They are inexpensive, but the shipping is expensive.  Maybe I should keep a few hundred here in the office to go out with the plots.
Rope Caulk. I understand some have used rope caulk, but I could never get it to work well in the cold, which is most of the year here.
Stick. Matthew Reynolds uses a stick or pvc pipe on the bag end and rolls the bag around it. He then clamps the roll off.   Along the long side he uses mailing tape with good results. The bag has to be even and smooth for that.
A guy could use a few tubes of Liquid Nails each bagging, but it takes some time to squirt out.
The joints or corners on all the systems take a shot of plywood panel adhesive (Liquid Nails) to seal.

Please add any others people have used with success.

I can see a published technical paper here with the results including vacuum hold duration comparisons and cost comparisons.

Metric

Virtually all new work is done in metric now. The work is created real world size and then plotted at some scale, metric or not. However there are some exceptions. I recall that some 15 years or so ago the US Coast Guard declared that all work submitted to them for review must be in metric. Within a month or so, the plans reviewers had told me that any plans submitted in metric would be returned without any action.

So, on the chance that a plan set is different than you prefer, I propose buying a dual format tape measure and this website, http://www.hocltd.com/metricalc.html
Again, most of the new work is metric and most of it has dual dimensions.

Latest

Between rush deadlines and supporting some 50 ongoing projects, the blog has fallen behind. As soon as I can surface for air, some of the topics will be:
Revisiting Post-Apocalyptic Boat Building.
Always new projects submitted.
Latest on sealing the vacuum bag.
Looking into PET foam.
The greater Seattle area has about a dozen relatively exotic KHSD multis building and sailing- lets look.
The cat projects in Africa and Estonia are ongoing.
I should catch up soon.

Plywood/Glass strength Comparison

How strong is glass compared to plywood? Here is a table comparing strengths with out of plane loads (like water pressure).

Plywood/Glass Thickness Conversion comparing bending strength. (Assumed 60,000 psi bending strength for glass and 10,000 for plywood)
Assumed that triaxial amount is on both sides of a core

Ply thickness Triaxial thickness Core

3mm ply equals     (12 oz)  400 gsm w/12 mm core

4mm ply equals     (17 oz) 600 gsm w/12 mm core

6mm ply equals      (22 oz ) 750 gsm w/12 mm core

9mm ply equals      (34 oz)   1150 gsm w/19 mm core

12mm ply equals   (2) (22 oz ) 1500 gsm w/19 mm core