Transom Edge

Designs for inboard or outboard power

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tclark
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Transom Edge

Postby tclark » Tue Jan 02, 2018 9:14 am

I have fiberglassed the hull of my Scooter and I applied EZ flllet along the edge of the transom in order to sharpen the edge. I read somewhere that it is important to have a 90 degree edge on the transom for performance reasons. Will grind that off to a nice edge tonight.

Are there any other areas of the hull where I should have a sharp edge? I rounded the chine and the tunnel chine for fiberglassing reasons, (about like a pencil) and just making sure I don't need to have any other areas where I should have a 90 degree or sharp edge of the hull.
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Scooter Glassed.JPG

tclark
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Re: Transom Edge

Postby tclark » Tue Jan 02, 2018 9:16 am

The picture I attached doesn't show the transom with the fillet material I added to sharpen the edge.

DSR
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Re: Transom Edge

Postby DSR » Tue Jan 02, 2018 10:33 am

Hi tclark,

The Scooter looks great!!

From my research on tunnel hulls, the tunnel chines should have straight sharp edges (and this becomes more of a priority as speed goes up), as the tunnel chines effect the tracking ability of the hull (like a keel on monohulls). There's more leeway with the outer chines, but I would personally sharpen the outer chines as well.

Thanks, :D
Dave
DSR Performance - Home of yet another jet TNT build :D
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viewtopic.php?f=23&t=29753

bobinpowayca
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Re: Transom Edge

Postby bobinpowayca » Wed Jan 03, 2018 2:04 pm

Hi, my 2 cents.. seems to me an edge the radius of a pencil is pretty sharp. Mine is about the size of a crayon - I think any sharper I'd be worried about the durability of that edge, or the coating staying on it. Bob
Bob
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Bill Edmundson
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Re: Transom Edge

Postby Bill Edmundson » Wed Jan 03, 2018 2:38 pm

I'm with Bob on this one.

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DSR
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Re: Transom Edge

Postby DSR » Wed Jan 03, 2018 6:31 pm

Hi guys,

I should clarify what I was talking about, and I apologize for being vague in my answer to your question tclark.

When I refer to the chines, and certainly the transom being sharp, it definitely can't be done to the point of being razor sharp. There does still have to be a small radius to allow coatings, such as epoxy and paint, to be able to adhere to the surface at those sharp edges without cracking or peeling. Typically on performance planing hulls, a radius of less than 1/16" is used and even smaller radii are quite common (especially on race hulls) to break the adhesion of the water surface and keep it from climbing the transom and tunnel walls, creating additional water drag. Sharp edges on the tunnel chines also positively effects the hulls tracking ability (more so with tunnel hulls having sponson pads with lower deadrise angles).

Again, how high a priority being given to sharpening the transom and the tunnel chines, and how sharp those edges are, is related to the intended performance you're going for, but even hulls moving at 25-30 mph can benefit from doing so, there just isn't as much of a benefit as there would be with a hull capable of 80-90 mph.

Thanks,
Dave
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

tclark
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Re: Transom Edge

Postby tclark » Thu Jan 04, 2018 10:19 am

Thanks for your replies. I think I will leave the transom fairly sharp and leave well enough alone of the chines.

I have noticed that I have some bad spots on the hull when it finally hardened, that I didn't notice when I was laying out the fiberglass. There are a couple of air pockets under the fiberglass that are smaller than a dime and I guess I need to sand them out and patch with a piece of fiberglass.

Additionally there are some bumpy spots in a couple of areas where it appears there is epoxy under the glass but no air, leaving a small bump. I can push on them and there isn't any movement and I don't see any air pockets. I don't know how this happened, I have a couple doze of these bumps. I suppose I should sand them off and it will go through the glass so I have more patching to do. Heavy sigh. I thought I had things laid out very flat but upon further review that is not the case. It is strange how I have most areas that turned out completely flat and smooth and others where there are bumps. I guess the glass gets pulled up by the roller or the glass is stretched and wrinkles are left behind. Very frustrating.

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billy c
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Re: Transom Edge

Postby billy c » Fri Jan 05, 2018 5:42 am

The inside of the chine (in the tunnel) needs to be sharpened as well as the transom. Outer chine slightly rounded about like a pencil diameter.
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