CS17 #370 Peggy-O

[Howard]

Mystery solved on the rudder. It does appear you used 1208 biaxial glass, but inadvertently left the mat side out. The mat does turn into a wild gelatinous mass that would leave a finish like the one in the photo. If put to the wood side, you would not have seen much, if any difference. Solution would be to sand the rough part down to get to the biaxial glass layer, ....... but other than a lot of extra work to get back to a smooth finish, I would see no harm done.

 

I did a lot of research into the 1208 biaxial glass cloth........why the mat? In most fiberglass layups, the purpose of the mat is to act as a cushion between layers of heavier woven glass cloth to eliminate any voids. The mat turns to mush to fill any uneven spots or voids between the layers. It also adds bulk (and weight) to the layup, but no real strength. For something like a rudder or CB, if you are only using one layer of glass for abrasion resistance, you would be better off without the mat layer. Say just 12 oz biaxial alone. On the other hand, if you were using two or three layers of biaxial cloth tape to reinforce a chine or bulkhead joint, you might be better of using the biaxial with mat to get a layup without the voids. Best outcome would be achieved by having the first or last layer without the mat, such that the side to fillet directly on the wood is cloth.....not mat.....and last or top layer facing out would also be the cloth......not the mat.

 

If you wanted to use the 1208 on a rudder or CB, again, mat in the layup would not help much, but would be OK, provided you put the mat to the inside. We now know what it looks like if you leave it on the outside.

[PAR]

Unless the appendage needs some reinforcement, there's no need for biax fabrics. If the goal is abrasion resistance, Xynole is the best choice, being 6 times better than regular 'glass cloth. Dynel is another good choice, being about 2 - 3 times better than regular cloth. Both of these fabrics use a lot more goo than regular cloth, but man they're tough. For general abrasion resistance and not a lot of weight, regular cloth, 6 - 10 ounce will do fine on a board. In fact, there's not much difference between 2 to 6 ounce cloth in terms of abrasion resistance, so small craft can use the lighter cloth and save goo and weight.

 

The use of mat in biax or triax "combo" fabrics (1208, 1708, etc.) is to promote a better bond with the coarse stitching and unidia's under it. These fabrics tend to have quite a bit of undulation about them in a laminate and the mat (as previously described) helps fill these potential voids for a better interlaminate bond. If just using a single layer of biax, you can grind off the polyester stitches when it's cured (carefully avoiding cutting the 'glass strands). The same is true if building a laminate of multiple layers, but letting each cure first. This saves some weight, as mat is a "bulking agent" and sucks up goo like I do beer.

[Dale Niemann]

Peter comment reminded me of something that I did forget to mention.  I have a custom made cabin for the whole area forward of the mizzen.  I have snaps on the outside of my raised combing which have worked very well for keeping out rain water since the canvas cabin falls outside the combing.  This is also the reason I will only flatten the combing aft of the mizzen.

 

Hopefully you can see what I am talking about in the photo.

 

dale

 

[LennieG]

Thanks all. Howard and Paul- all makes sense and explains it.

Dale- down to 2" front center, noodling around with coaming look. Sure am glad I am dry fitting first!

David: Definitely dry fit a template IMO as I have wrestled with it for two days and the " peg board without holes", which is pretty pliable stuff, did not fill the voids well at all in the corners. I was glad I wasn't playing around with stiffer wood with epoxy kicking off. I still have another day of wrestling with the template, dry fitting and finding ways to clamp the corners. None of it seems as simple as I imagiined, but it will work out with patience and imagination.

[LennieG]

Inching towards completion with small steps behind me. Finished with coaming template, ordered 1/8" thick mahogany strips for coaming, framed out hatches, sanded off rudder, and added extra support for bend in coaming for better clamping and other misc. Closing in on it.

[PAR]

When you dry fit the mahogany for the laminated combing, use a heat gun and get those corners good and warm. Heat more than anything else is what will do it. Once you do get the pieces clamped into place, wet them down with some denatured alcohol and hit them with more heat a few times, which will help them remember their "set" when unclamped for applying goo. Once bent, the wood will want to remember this shape, so the more time you can leave them in the setup, clamped, the more set the cells will remember when you have to remove them.

[LennieG]

Paul-

Thanks very much. Having wrestled with 1/8" marmite or pegboard, which is fairly pliable, during template process, I can tell that the dry fit wil be interesting. I was originally planning to build the laminated coaming on a bench and then install, but feel it best to laminate on boat as rigidity would be my enemy. with the various twists and turns.

Is the heat gun basically a hair drier or different animal?

Thanks for your comments. I will follow them. I assume the first layer will be the hardest.

[PAR]

A heat gun is much hotter than a hair drier, usually the cheap ones will have two settings damn hot and really hot. You'll want the really hot setting (typically 500 - 700 degrees) and keep it moving. All the layers of the lamination will piss you off and fight nearly equally.

 

Sometimes it's handy to setup a temporary jig to help the bend, something like "L" brackets that you can use to roughly hold the stock in place, as more pieces get shoved in. Once all are in relative position, clamp them to shape. The L brackets will permit some wedges to be driven in, to compress the laminate stack the last fraction of an inch. Lastly it's very difficult to bend stock in two directions at once (vertically and horizontally, for example).

[LennieG]

Thanks again for the thoughtful response and the great, entertaining writing style. Appreciate both.

[LennieG]

Had a fantastic day! Bill Palumbo worked with me for a full day.....thank you Bill! (DocPal , CS17 Petunia). We got the boat ready for coaming, mahogany cut , jig made, pieces clamped for memory and obedience. We didn't break any! Heat gun worked, mahogany pliant, alcohol rubbed etc......

Thanks to Bill and Paul for the guidance and help.

[Dnjost]

Awesome guys.  Hope to catch up to you with my build!  Thanks for leading the way with this aspect of the build.  

[Don Silsbe]

LennieG,

Is that a fir plywood c/b trunk? If so, I suggest you sheath it with some 4 oz cloth. I have experiences RAMPANT checking on a little dinghy I built years ago. I coated it with West epoxy the first time, and MAS epoxy when I refinished her a few years ago. I'm planning to sheath it with 4oz this spring.

[LennieG]

The question confuses me Thrillbe.....CB trunk not shown in pics. The CB trunk is mahogany marine ply that came with the Kit, and I did sheath the inside w 10oz glass which is what I owned.

[LennieG]

David-

The only reason you won't catch up with me is the MA temps. The coaming is working out and the Saplele mahogany lumber is pretty great as far as bending without breaking. I had 6ea 1/8" 8 footers milled for $80. The sapele is pliable and workable. A friend and I got the first two layers on the boat today without issue, and 2 to go. I am not sure if it the most attractive mahogany but price and workability outweighs other considerations for me. I will spend another $40 for side pieces once I know this is going to fly. A new sheet of marine ply would have cost same or close all things considered like gas and/or delivery. Installing on the boat is a two man job. Further, I was not able, or didn't dare, to get the angle outboard at the corners. Another words, as you come forward from aft deck with the carlins or coaming, the angle is outboard ( top is outboard vs bottom of carlin or coaming). Plan calls for that outboard angle to continue thru corner and then get vertical at front section. Didnt happen. The corners are either vertical or slightly inboard. I did not dare to force tops out at corner, nor did I have adequate clamping leverage. All in all, working out as far as I know.

[PAR]

I'm glad you got 'er done, looks pretty good too.

 

Sapele (Entandrophragma cylindricum) isn't technically a mahogany (Swietenia macrophylla), though it has some broad (Meliaceae family) relations which partly explains the marketing ploy. Because of it's interlocking grain, it bends better than most of the true mahogany's. This stuff should smell like cedar when you cut it.

[Docpal]

Thrillsbe,

I think the picture you think is a centerboard trunk is really our bending blocks which were then screwed into a piece of 3/4" Fir plywood to make up the bending jig for the coaming laminations

[LennieG]

Thanks Doc- I was going to clear that up for Thrillsbe myself as it dawned on me later what he was seeing.

[Hirilonde]

I'm glad you got 'er done, looks pretty good too.

 

Sapele (Entandrophragma cylindricum) isn't technically a mahogany (Swietenia macrophylla), though it has some broad (Meliaceae family) relations which partly explains the marketing ploy.

 

I would bet that the common name Mahogany is the most misused name in the lumber industry.  My local yard calls Dark Red Meranti (Shorea Platycladus) Mahogany.  I sometimes think it is just a marketing ploy as Paul points to.  Other times I think it is a dumbing down for the sake of the vast majority who don't really know much about the characteristics of wood and why it matters.  Saying Mahogany means the wood is reddish in most cases.  It is sad, because Meranti, Sapele and all the other reddish woods have uses and are beautiful.  Let's use them according to how their characteristics meet the needs of our applications and call them what they are.  Unfortunately it is hard when the industry itself is misleading us.

 

BTW, I am getting 2 sheets of Sapele BS 1088, the rest being Okoume just 'cause I think it will be pretty for the decks and transom of my Lapwing.  I like the looks a lot too Lennie.

[LennieG]

Point well taken Dave and Paul. To illustrate the difference, I recently purchased some "mahogany 1/4" " for my hatch tops along with coaming sapele. Not much wood or cost. It was to go on top of my " mahogany" left over from rub rail purchase of 18' pieces. After I cut it today it was obvious that the lumber was different species ( the new being sapele, the old being South American mahogany). I like either by itself, but was frankly not comfortable with mixing them on the same small piece. You'll see the difference in photo. For fairness, know that the base has some epoxy and the top doesn't....I know that finished they would look closer.

Anyway, I quick call resolved the issue and the new lumber will be ready in a day or so. There was no deception or malcontent on my suppliers part. When I ordered the original lumber for inwales and rub rails the only 18' pieces were South American, but my recent orders were smaller pieces and he was responding to my prior bitching about prices so trying to keep the cost down. All resolved but I point it out so one can see the difference.

[PAR]

There are about 40 sub genius of mahogany, so it easy to see how it gets misrepresented. There are only a handful of these in the common marketplace and all have some particularities about them, which once recognized, makes it easy to identify. Red Shora (lauan/meranti) is often called Philippine mahogany and it does look somewhat like mahogany, but if you know the difference, it's an easy pick. The one thing to look for is the coarseness of the grain and the silica content, which reflects and changes the color of the grain as you eye passes over it. This is one of the things I like about real mahogany and it's ruined if you stain the wood, which is why I use a lot of natural finished mahogany.