Radon Transom Replacement

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
Fuzz
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8920
Joined: Tue Aug 02, 2011 4:23 am
Location: Kasilof, Alaska

Re: Radon Transom Replacement

Post by Fuzz »

Wrapping glass over the stringers and out onto the hull without ending up with air voids can be tough to do. I have done it when installing stringers in 32-40 foot boats but I have helpers. Tabbing the stringers in and then capping them is much easier if working by yourself. I would not get too worked up over having the stringer side perfectly smooth. After curing a quick pass with the sander and maybe one pass with a fairing putty would be good enough. JMHO :wink:

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Radon Transom Replacement

Post by fallguy1000 »

Too many turns makes life hard. Pulling on glass cap and keeping the corner fillets good on the bottom is very hard for even someone with years of laminating experience (me).

Tab and or glass the sides, then let it cure for a few hours or sand and cap the next day.

I'd prefer to do the sides and tabbing in the same go, then cap the next day, but also depends on materials you have. Avoid all hardpoints. No edges should stack; almost always.

So, if you have to do the sides for material limitations; you would run to the top and step back an inch with each piece.

I may consider breaking the rule on the bottom, but only because it really won't matter. At the top, the cap would be applied; probably two pieces minimum of 1708 and also staggerred into the other steps.
My boat build is here -------->

viewtopic.php?f=12&t=62495

bigtalljv
Active Poster
Active Poster
Posts: 398
Joined: Mon Jun 25, 2012 12:41 pm
Location: Central Coast CA

Re: Radon Transom Replacement

Post by bigtalljv »

Thanks guys. I really appreciate the tips on having help or working alone, I’m alone most of the time so I will adjust accordingly.

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1662
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: Radon Transom Replacement

Post by OneWayTraffic »

Aside from the workload issues I'd use 45/45 for tabbing, and unidirectional or 0/90 for capping. Fibers running the length of the boat just makes sense to me on the stringer tops. On my boat the sole is directly on the stringer, making a box section which has a similar effect.

bigtalljv
Active Poster
Active Poster
Posts: 398
Joined: Mon Jun 25, 2012 12:41 pm
Location: Central Coast CA

Re: Radon Transom Replacement

Post by bigtalljv »

OneWayTraffic wrote: Fri Aug 05, 2022 4:14 pm Aside from the workload issues I'd use 45/45 for tabbing, and unidirectional or 0/90 for capping. Fibers running the length of the boat just makes sense to me on the stringer tops. On my boat the sole is directly on the stringer, making a box section which has a similar effect.
I’ve been thinking about the unidirectional fabric. If yes I can’t make the stringer too strong or too stiff? Mostly I need to find out if my local place can get it and if the can get it usable tape widths, 6-8” I think. I really don’t want to cut up big sheets of it.

Well I got the fist stringer tacked in today, lined it up and hopped it in place in a few places. Had some spacers in there so it was suspended above the hull.
Attachments
56DA2A93-0143-4F74-A9C9-EDAE6FEB8BD2.jpeg

Fuzz
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8920
Joined: Tue Aug 02, 2011 4:23 am
Location: Kasilof, Alaska

Re: Radon Transom Replacement

Post by Fuzz »

Sounds like god progress is being made :wink:

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Radon Transom Replacement

Post by fallguy1000 »

Actually, uni is sort of wrong.

Half of the fiber orientations offer no benefits.

I didn't say anything because it doesn't matter much. The cap only matters if the cap provides side fiberglass to the stringers.

Otherwise, the cap is largely a seal to prevent water getting in...thus my failure to speak.

The cap glass needs to be thick enough so a ding doesn't make a hole that can be a source of water.

The cap needs to provide some strength, but not a lot unless the stringer core is not strong.

Personally, I'd go about 3 layers of 1708 or so.
My boat build is here -------->

viewtopic.php?f=12&t=62495

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1662
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: Radon Transom Replacement

Post by OneWayTraffic »

I was talking based on Gerr pg41 and 47. Biaxial for tabbing frames and panels, 0-90 for stringers. Those are glass over foam stringers though, not tabbed in wood stringers. Agreed that it shouldn't matter at all if wood is providing the strength. Just cap it with something so you don't get splitting. Come to think of it, if capping is the primary purpose I'd prefer 0-90 or biax to unidirectional. Better vs splitting as the fibres are running across the stringer. A layer at 0 degrees will add more stiffness to the hull, and if it's unidirectional glass in epoxy should be stiffer than an equivalent extra thickness in wood.
Attachments
Elements of boat strength pg 47.png
Elements of boat strength pg 47.png (70.19 KiB) Viewed 727 times
Elements of boat strength pg 41.png
Elements of boat strength pg 41.png (168.29 KiB) Viewed 727 times

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Radon Transom Replacement

Post by fallguy1000 »

The 0-90 is for layup or sides of the stringer, but the 0 strands do nothing on the cap. One could argue they keep the stringer from twisting I suppose. But the argument is pretty weak as the 90s would do more.

The basic idea is to keep the strands operating against the forces that present on the part, and in tension is best.

In the case of a stringer, what are the forces acting on it?

They are the transfer of transom loads to the hull or largely a force coming from the transom to the bow. And the 0 strands in uni are laying in the same direction, so they do very little.

But, some forces act on the hull from the water below in the case of high seas or impacts to waves.

The portion of those forces in the Y direction would be perpendicular to 0 strands in uni. And any forces working to bend the boat, on the trailer, for example wpuld act against the stringer in the Y as well. This is why Gerr advocates for uni. But, take a 3/4 x 3 ply stringer laminated together and suspend it on the ends and deflection test it. My guess is it won't register deflection until about 500#, maybe more, and that the uni on the sides will be incremental improvent to the numbers. But that is what the uni does. It reduces deflection in the Y when placed on the sides of the stringer because the fabric tows are in tension either way.

Now, consider the 2.25" cap. Adding glass to it will offer very little resistance to upward forces in the Y direction, because the fibers are not in tension. They would be in tension downward.

So many words to explain the cap doesn't matter.

But hopefully somewhat edifying. Pictures would be better.

To compare biax, take a say 8" section of stringer, 25' long. Biax fibers travel along the sides of the stringer and are how long? 8x1.414 or 11.3". By comparison, the tows in the uni extend the entire length of the stringer, ftmp,

Now, why don't we tab with uni?

The tabbing is for shear. We don't want the stringer to break off the hull. In this case, the 0 strands in uni do absolutely nothing. 90 strands do the best work. But 45 strands offer resistance to shear in two directions, or all shear forces in all directions, whereas the 90 tows in uni offer best perpendicular shear resistance but parallel.
My boat build is here -------->

viewtopic.php?f=12&t=62495

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: Radon Transom Replacement

Post by TomW1 »

I will keep it simple you need to use 45/45 biax to connect the stringers and frames to the hull. They are both subject to various forces that 90/0 cannot account for. The 12oz biax tape will do so.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests