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Dishing the chine questions

Dishing the chine questions
September 09, 2016 04:10PM
Hi all! My name is Vasili. First boat attempt. Have built furniture, but this is a different animal. I want to turn the Buffalo boat into a skiff by widening the front and rear transoms a bit, and dish the chines. I fish in Michigan. skinny water, and a few riffles to deal with.

1. When I dish the chines which end gets attached to the boat floor, dished or straight end?
2. Will I need to extend the the side panels and floor? I will be widening the transoms a bit, but does the combination of that and dishing the chines necessitate lengthening the floor?
3. Has anyone used Roseburg marine plywood? Can get it local at Menards slightly cheaper than hydrotech and no shipping costs
4. Sandy has talked about thicker plascore and less glass, was thinking 1" plascore bottom with 2 layers fiberglass inside and out

Thanks for any answers!! I'll update with pictures gonna start mid October
Re: Dishing the chine questions
September 09, 2016 09:17PM
Reducing Rocker <== dishing talk here

The dished out edge is the chine, so that edge is what attaches to the bottom panel. One way to do what you want is to make adjustable ribs as per the discussion on New Hull Designs

Then you can cut out the side panels as the plans call for. Then dish out the chine as above, perhaps as much as 3" or even 4" inches at the middle. Then attach side panels to (adjustable) ribs. Then attach transoms. Then play with bottom widths and side angles, by fiddling with the adjustable ribs, until you get a boat shape you like looking at. Then turn it into a boat.

You won't need to make the side panels longer.

3/4" inch Plascore is fine but 1" inch is stiffer, without weighing much more. 2 layers fiberglass is not enough. You need 4 layers outside bottom on Plascore. Or more. Plywood has its own stiffness so with plywood you only need to skin with a small amount of glass. Plascore has no stiffness so with a honeycomb core layup the stiffness comes from the glass rather than the core.

You can always add more glass.

One more thing to think about. If you want a boat that floats in the skinniest water you want to reduce rocker AND make it wider. You might want to use the Buffalo Boat dimensions as a starting point, making the side panels as specified, then dish them out, and THEN play with the adjustable ribs to make a boat that might be as much as 56" inches wide. Or more. The Buffalo Boat is the easiest one to modify. The best way to work out modified Buffalo Boat dimensions would also start with temporary transom ends made from CDX plywood or chipboard, so you can try out different transom dimensions too.

That's how I design everything--experiment. Look at it. Cuss. Start over and change the widths and angles a bit. Look at it again. Repeat until your teeth are all ground away or until you get a good looking boat.

It's always a bit nerve wracking to design your own boat because you mind tends to worry: "Will this boat suck?" But they almost never do. An extra wide Buffalo Boat will float in some very skinny water. Reducing rocker will give it even more flotation. But you will pay a maneuverability price. Flat boats are slower to turn.
Re: Dishing the chine questions
September 10, 2016 04:46AM
Thanks Sandy! I'm good at starting over and cussing. The guides around here pole the ausable river boats, so turning won't be a huge issue. So even with the 1 inch plascore I'll need 4 layers of glass? I remember reading thicker plascore lends to less glass, or is 4 layers less than normal? Thanks for all the good info!
Re: Dishing the chine questions
September 13, 2016 02:22PM
Just to add my 2c. I am in the planing and gathering stage of my next boat and part of the plan
is of coarse material choice. So far I have not seen or heard anything good about Roseburg marine fir plywood and its only about twenty bucks less than good old hydrotech...why risk it.
I have to drive a hundred miles one way to get either one or pay to ship it as well !
As far as the bottom is concerned , strength is a key factor so skimping on the glass layup with the plascore is not a good option for the rivers I float...read lots of rock gardens to tend to !
I would rather do a little overkill during the build than have a failure in the middle of nowhere .
Re: Dishing the chine questions
September 13, 2016 02:36PM
Plascore makes a fine bottom, whether married to plywood above or more plascore. The issues are not strength or weight so much as moisture. Plywood soaks up moisture like a sponge. Some traditional framed boats get significantly heavier by the end of a long season than they are at the beginning. For stitch and glue plywood bottoms the problem can in some ways be even worse.

Plywood skinned in fiberglass tends to soak moisture far less than traditional boats. But it does soak up some, usually at damaged areas of the chine. And then--because of the fiberglass skin--that moisture can become trapped and difficult to dry out. All plywood stitch and glue boats need to be patched regularly to keep that from happening.

Thank you Plascore. A Plascore bottom married to stitch and glue plywood above makes a damn good boat that is easy to build.........where you can even start to get lazy about patching chine dings. Why hurry? Why wurry?

Too little glass on the outside bottom makes it too easy for the outside skin to break. The consequences of those skin fractures aren't all that bad. But still. Why be cheap? Use plenty of glass on the outside bottom.
Re: Dishing the chine questions
September 14, 2016 07:15AM
I'm convinced. Plascore US headquarters and a hydrotech distributor are a couple hours away from me, I don't mind the drive, both are near great steelhead rivers. But my question regarding fiberglass on the plascore isn't about money. Sandy mentioned in a previous post using thicker plascore and just enough fiberglass, I'm guessing 4 layers is the minimum outside on plascore. What's the minimum on the plywood? I want to save weight and end up with a boat that is just stiff enough.
Re: Dishing the chine questions
September 14, 2016 12:34PM
How many layers depends some on how heavy the glass. I used to buy 10oz fabric 50" inches wide because it was the thickest West System bought. But after talking to Larry at Raka (Larry is now, like me, retired) I realized the best glass is what Larry has on sale. Use that and make it work. I bought an entire roll of 3.5oz 38" inch wide fabric because it was a discontinued line and I got it for a song.

Layups are a subject with never ending complexity. I won't even talk about Kevlar. I try to keep my plans bare bones simple. If hotrod builders want to elaborate on what I suggest that's great. But complexity is not what I try to offer.

On the outside bottom you primarily need abrasion resistance. You want to be able to scrape over a rock with minimal damage. 2 layers 10oz over plywood is a first year minimum. Add at least one more layer for Plascore. You'll be adding a new layer a few years down the road. Which is roughly/vaguely equivalent to four or five layers 3.5oz. None of this set in stone. More layers of lighter glass is stronger than fewer layers of heavy glass.

Plywood has stiffness in its native state. Plascore does not. Not much anyway. But both materials become a "stressed skin panel" when covered with glass, which increases strength and stiffness considerably. The greater the distance between the two fiberglass layers the stiffer it is. Stressed Skin Panel stiffness increases AS THE SQUARE of the core diameter. So for the finished bottom panel 1" thick Plascore is considerably stiffer than 3/4" inch, without increasing the weight by much.

I've never used 1" Plascore. I bought 12 sheets of 3/4" a few years ago and then bought 4 more. And now I'm down to my last 4 sheets. I use what I have.

I'm 68 and I'm having health issues. Two eye surgeries this year alone. It's hard for me to get the driver bit into a Torx screw now, without driving a dripping red hole into my finger. Hard to see WTF I'm doing in the shop in general. My current boat hasn't changed in half a year because of the surgeries. I hope to finish it this winter. It will probably be my last boat.

I'm easy with that. I'll move onto other things. How many boats does a guy have to build anyway? I've done my part. All I want is rowing and maintenance from here on out.
Re: Dishing the chine questions
September 14, 2016 12:59PM
Jeremy Christensen, who sometimes participates here, built a traditional 48" wide 18' feet long Briggs with 1" thick Plascore for the bottom panel. Jeremy did a hell of nice job. I rowed that boat briefly, on the Green. The floor was impressively stiff. That boat was annoyingly side-to-side tippy. Everyone said so. It's all we talked about at the first night after Jeremy showed up. I think he sold that boat and moved on.

There are plans out there somewhere for a 54" inch wide Briggs, which would be a lot better that 48".

The original Woody Hindman boat was 48" wide and made with 16' foot or 192" inch side panels. That's a final width to side panel length ratio of 4:1.
That boat is commonly refered to as a 15x48. It's made from 16' foot side panels but the finished boat ends up about 15' feet long.

What most people refer to as a seventeen foot boat is made with 18' foot side panels. That would scale up to 54" inches wide, to be the same boat as the Hindman. That's what most people refer to as a 17x54. The 17x54 is common and well liked and well respected West Coast boat. It's the same boat as the original McKenzie scaled up proportionately, so it's a bit longer and wider.

The Briggs was made with 19' foot side panels (do I remember that right????) So, for a 19' side panel boat to have a traditional width to length ratio it would have to be 57" inches wide. The traditional Briggs is a looooooooooooong skinny boat. It will drive you nuts trying to keep it from constantly tipping.


Why is the Briggs like that? Martin Litton asked Keith Steele and Jerry Briggs to build him some long dories. Instead of scaling up proportionately they just chopped their existing 15x48 boats in half and added a 4' foot long parallel chine tube in the middle. And that's how the infamous "flat spot" got born.
Re: Dishing the chine questions
September 14, 2016 01:26PM
All you need is one layer inside and outside on the side panels with just enough resin to bury the weave and get a smooth finish after wet sanding.
Re: Dishing the chine questions
September 14, 2016 01:37PM
For side panels made from plywood one layer of 3.5oz is fine, inside and out. For an all fiberglass all Plascore boat you'd need more glass. One layer is fine for plywood.
Re: Dishing the chine questions
September 14, 2016 08:33PM
Thanks guys!! Got some info from Raka today. Ordering soon.
Re: Dishing the chine questions
September 15, 2016 09:45PM
That why (what Tungsten said) I said the issue was not weight or strength or stiffness. It's all about moisture, which is a big problem with plywood bottom panels, but not with Plascore
Re: Dishing the chine questions
September 16, 2016 08:18PM
Tungsten is a good resource for layup technology. Do a search on his name, here in this forum and several others, and a lot of good information will come up.

I do my best not to recommend anything but the bare bones most simple solution. That makes my life simpler, keeps me out of arguments and covers my bases. I quit using Kevlar a long time ago. It's good strong stuff but way to expensive.

I do use biaxial tape from Raka on chines. It can be hard to wet out without a "fiberglass roller" during the layup. If you do buy biaxial tape I recommend a fiberglass roller too. They aren't expensive. They look like a short paint roller with a series of round metal discs on the roller instead of foam or knap. A roller helps to get the air bubbles out of difficult layup. like biaxial tape on the chines.
Re: Dishing the chine questions
October 09, 2016 02:22PM
vpsihop@hotmail.com Wrote:

> I want to save
> weight and end up with a boat that is just stiff
> enough.

I you are going to start using plascore I would forget about the weight issue. On a plywood bottom you are going to use 2 layers of 10 oz glass at least. Now add 2 more and the epoxy you need and the extra glass is not enough think about. The plascore is so light you don't need to worry about extra glass. On class III water 3/4 will be fine but from now on I will move to 1 inch. I have never seen any thing come even close to getting through 3/4 so 1 inch with lots of glass will be very tough and still light as compared to all wood or a molded polyester/glass boat.

As for dishing out the chine, I'm not sure what you are after. The HD has a 56 inch bottom, most are 48 inches. Are you looking to move to 60 or 62? Be carefull when making changes to the bottom profile. If you make changes by adding rocker, you will lift the stem and stern out of the water and the result, as Sandy mentioned is you will draw more water. For low water floats you want wide and flat on the bottom to float high. We are talking about fishing boats here, the big waves of Class IV stuff is a whole different set of issues. A good flat bottom stable fishing platform which floats high will be find in Class III water.
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