Midway Plywood Update

I just got back from Midway Plywood in Lynnwood, WA.  www.midwayplywood.com/

They have supplied many of my plywood/epoxy projects including the two Lake Victoria ferries. I had gotten a report that the 3mm plywood (2.7mm actually) was such poor quality that it was not usable. I just bought some very good sheets, so this shipment is better. It is Seal Brand which I have used before. The price has gone up about 50% in the last 6 months to $17.95 per sheet before tax.  It is about half the price of 4mm BS-6566 plywood at Edensaw Woods. http://www.edensaw.com/

I have not D790 tested it yet.  Possibly Thain Boat has.  I’m guessing the numbers would not be as good as BS1088 but close.


Why Epoxy is Preferable to Vinylester and both are Preferable to Polyester.


I always assume that everybody knows the information in the article below but I just was brought up short, so it may be time again. A true believer over at multihull_boatbuilder forum sent me a note telling me that everytime I point out one of Derek Kelsall’s technical mistakes (and there are so many; he is big polyester fan) “people…believe in your expertise less and less”.  I did find out that he is unaware of the below and not interested in it. It won’t be the first time that true believers wished I would stop pointing out what I see. Again, because I think it is so important to having a good vessel.

There are many good reasons to use epoxy instead of polyester.
First, stretch to failure. Glass fabric has about 6% stretch to failure. So does most room-temperature epoxy, and many vinylesters. Polyester stretch to failure is, everyone? About 1%. So in tension, the glass is only loaded to about 17% of its strength before the resin matrix starts to break apart and become a necklace.

Polyester will be bonding with water throughout its life, and it will gain surprising weight from that water, while losing strength properties. If I may quote from a D570 water weight gain test, “The orthophathlic casting had more than a 2.5% weight gain after 4 days, then showed a weight loss on the 7th and 14th days. That means the polymer is being broken down, solubilized, leached out of the composite, and replaced with water.”

The biggest benefit of epoxy is that epoxy is more forgiving during construction. Get the mix ratio right and you are there. With polyester, or even vinylester, one has to vary the MEKP level and vary the N,N-DMA level, oppositely, as a function of temperature change. Or, also, vary the BPO level and again vary the N,N-DMA level oppositely, as a function of temperature. The catylist/promotors have to be done exactly right to get a good degree of cure. The catylist/promoters will have amounts of down to fractions of a percent. Those amounts must be very precise if good results are intended.
Also, if the part is stored at less than 10C it may never cure fully, even with a later post cure. Using epoxy, you can improve the laminate properties with a post cure, almost always.
Interplastic Corp. has some great papers on this, which I am quoting from. Specifically, Proper Cure of Vinyl Ester Resins and A 15-Year Study of the Effective Use of Permeation Barriers in Marine Composites to Prevent Corrosion and Blistering.
I’ve never been able to afford a temperature controlled shop, so this
matters a great deal to me.
Until someone is using a Barcol hardness tool or even better, a D790
flexural strength test to prove it, I don’t want to hear how a laminate is acceptable with any or all the above conditions off, just because the lay-up looks good.
The point is if the temperature was too cold when you did an
epoxy laminate, you could bring it up to close to 100% cure later.
If you, for example, do a polyester laminate at 15C with 1% BPO and 0.3% N,N-DMA, you will have only an 80% cure and it probably cannot ever be improved.
That same formulation however will give 96% cure at 25C.

Most room temperature cure epoxies post-cure at around 65C to 70C. Static properties increase with the cure, and so does toughness against impacts. Epoxy can accrue the benefits of a post cure but polyester and most vinylester  will not be improved by a post-cure.  You got what you got.

Blisters are also a huge issue. With polyester, especially with orthophthalic resin, as Terry McCabe of Interplastic said, “Its not if it will form blisters, but when.” The useful paper again is “A 15 Year Study of the Effective Use of Permeation Barriers in Marine Composites to Prevent Corrosion and Blistering“. Aand again, Interplastic.

Shelf life is another issue. The useful shelf life of epoxy resin is years. Hardner has a shorter shelf life though it is still good for years. Both vinylester and polyester components have a shelf live of just months. If your project gets interrupted, that can cost you if you did a bulk-buy to save money.

  In an issue of Multihulls Magazine, Tom Pawlak notes several other shortcomings of not using epoxy resin, including excess shrinking of the part. That is more significant than simply the parts not fitting. Excessive shrinking sets up what is called residual stress within the part. That is stress between the various layers that are oriented different directions. The result will be earlier failure under less load.

In conclusion, both epoxy and vinylester are much preferred to polyester. Structurally, epoxy and vinylester are close in properties. Epoxy however is much easier to work with, and is much more forgiving.

More Cat 2 Fold

Several people have visited with Brian on C2F recently.
See http://members5.boardhost.com/lamanzanilla/msg/1391418285.html

and this from Dr. Peter; “BTW, I spent a day last week on Cat2fold, in La Manzanilla, Mex. Now owned by a Brian Charette,. He cruises it on the Pacific side of Mexico and puts it on dry land in San Carlos, Mex, in the summer while he builds straw-bale houses in Wyoming and Idaho. One of the reasons he chose the boat was that he could fit in the boat- he is 6 foot 7,
blonde, rasta hair, very hip, 42 years old, lady-killer kind of dude.
Has two kids 8 and 11 who cruised with him for a month this year. Their
top speed was 18 knots surfing under bare poles. We did about 11 during
the day in about 18 ambient wind. It has to be the easiest smoothest rig
to run around with. I was so happy to give it a whirl because that is
the configuration I think I would end up with, paired to a big outboard,
once I get really old. So I thought you would appreciate an update on
one of your really original boats!”


Charter Cat for Sale

This 36′ x 24′ daycharter cat is for sale.   Owner hopes to sell soon. 

Built using CM plywood epoxy construction with cored decks.
pair of new honda 15 hp high thrust with 20 hours each.
Lefiel mast, boom and bowtube
Teleflex steering
Harken hardware
Staaf sails
Kick-up rudders
Portabote tender
KED lights
Life Sling                                                                                                                                   Lifelines                                                                                                                                           2 Bruce anchors

Seller wants $90K, down from $100K. It does have USCG stamped plans for 24 pax and out 20 miles, but owner never did go for COI. I can do that. I suspect it only needs new application for inspection, deadweight survey and stability calcs.  I will assist with those.
It is demountable and does all fit into one container except the mast. Is here in Washington state but can be shipped anywhere.  Contact me at 206-284-6346 or at khughes@multihulldesigns.com





Thinner Cabinet Foam-Half Inch Foam

I was at Uresco, the Owens-Corning distributor, today and saw a product that I have not seen before. That is half inch thick pink foam. I have advocated using the 1” pink foam for lightweight cabinets but wished it could be thinner. Here it is. Its the best choice that I can think of for lightweight shelves and cabinets. Surely it is as light or lighter than Tricel core, and much less cost. Also, the edges are much easier to finish. Vacuum bag thin plywood or even fiberglass onto the faces. The result is shelves for example weighing only ounces. That is one inch foam on the lower half of the load below.


Rhino Linings Epoxy

John asked me to look into Rhino Linings Epoxy. http://www.rhinolinings.com/divisions/epoxy
I seem to remember that Jeff from Jeffco Epoxy works for them now. I was given his email and phone number, but he never responded. I also seem to recall that he had actually gotten a USCG approval for a fire retarding epoxy,  without additives. I seem to remember also that the Jeffco Epoxy had a variable hardner ratio. Maybe someone here knows more about these.
I do not see a stretch to failure percentage on their online data sheet. The HDT is very high so I suspect the product is brittle. I have applied for more data and a sample. Maybe I will learn more.

Talking to Corporate at Spacebags

I see a lot of use for Spacebags that are larger. They are so cool when they work. I did 4 baggings in two days in weather just above freezing over the weekend. I ran the vacuum maybe 3 minutes total.
The largest bag made now is 3’ x 4’. I contacted customer service at Spacebags to see if I could talk to development about bigger bags. NO!

Unless I have a patent on one (?), they are not in any way interested. Why would I patent one? I just want a bigger bag. I guess it comes with corporate size, but it is always interesting to see full-on corporate ossification. They don’t even want to discuss another size product or new use.


Stephen Crane on Resin

Stephen mostly works with the big boys in volume production marine, wind blades, and aerospace. As a result, room temperature cure epoxy is barely on his radar. That is very different from my DIY guys and the custom builds who both use the above epoxy. He speaks highly of Derakane 411 which is a vinylester that he calls more epoxy than vinylester. The big boys have less concern about impact resistance than cruisers and charter guys do. My one concern with the high temperature epoxy is the brittleness. I will keep studying with Stephen’s information in mind.