Fiberglass Thru Hall Repair

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Tgornik
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Fiberglass Thru Hall Repair

Post by Tgornik »

Hello,

1973 Trojan F31 Fly Bridge w/ Twin LM 318 Raw water cooled (But not too important for this post.)

Pre-launch Hull inspection over the weekend found the marina blasted and chunked off the wood around of an old depth finder thru hall.

I'm looking for feedback on the proposed repair method and any additional tips and tricks.

Background:
I plan to use many of the tips and trick found here:
https://theboatgalley.com/filling-in-a-thru-hull/

I also plan to mimic the process described here:
https://www.epoxyworks.com/index.php/th ... rs-takara/

My Main question is the 12:1 ratio. Is the "1" the
-thickness of the hull (assume a 1" thickness, then the taper/prep area is 12" wide?)

or

Diameter of hole repairing- (assume 3" diameter then the prep area would be 36"?)

question 2: Taper both the inside and outside to meet in the middle?


Also, I'm slightly concerned about 'tapering' the hull all the way through the thickness... These Trojans are THICK. I understand the theory of a tapered hole on both sides to keep the 'plug' from ever coming out, but is it really necessary to take the parent material (original hull) all the way down?

Attachments:

Thru hall 1- as viewed from underside of boat
Thru Hull 2 - as viewed from inside
Thru hall- underside far


Any comments on the process?

Im planning to use

https://www.fibreglast.com/

or

https://www.westsystem.com/

Best,

Tim
Attachments
the plan
the plan
Thru Hull Sketch.PNG (72.52 KiB) Viewed 7208 times
under side far
under side far
Thru hall_low.jpg (97.21 KiB) Viewed 7208 times
as viewed from inside of boat
as viewed from inside of boat
thru hall 2_low.jpg (107.11 KiB) Viewed 7208 times
as viewed from underside of boat
as viewed from underside of boat
thru hall 1_low.jpg (69.16 KiB) Viewed 7208 times
"You're gonna need a bigger boat!"

1973 Trojan F31 Flybridge W/ Twin Chrysler LM 318s
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prowlersfish
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Re: Fiberglass Thru Hall Repair

Post by prowlersfish »

The 12 to 1, I believe refers to the hole Diameter. I also believe 12 to 1 is way overkill for a small hole like this. I would taper the hull a bit and grind some around the edges ( not as deep as your drawings ) fill and glass over. I have done this more than once without issues.


Another easier but more costly way is get a new Fish/depth finder with a new transducer and install it. You can get a flush mount and not worry about the blocks. Get one with a built-in offset I just install a B60 on mine 10-degree offset worked fine.
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Tgornik
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Re: Fiberglass Thru Hall Repair

Post by Tgornik »

prowlersfish wrote: Mon May 01, 2023 12:03 pm The 12 to 1, I believe refers to the hole Diameter. I also believe 12 to 1 is way overkill for a small hole like this. I would taper the hull a bit and grind some around the edges ( not as deep as your drawings ) fill and glass over. I have done this more than once without issues.

Thanks and completely agree...

Another easier but more costly way is get a new Fish/depth finder with a new transducer and install it. You can get a flush mount and not worry about the blocks. Get one with a built-in offset I just install a B60 on mine 10-degree offset worked fine.
Thought of this but would still have to mess with the diameter of the hole so just decided to plug and start over..

Thanks again.
Tg
"You're gonna need a bigger boat!"

1973 Trojan F31 Flybridge W/ Twin Chrysler LM 318s
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captainmaniac
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Re: Fiberglass Thru Hall Repair

Post by captainmaniac »

First off, I align my thoughts with prowlersfish - I am very focused on retaining history and keeping my boats as original as possible, but my mindset has always been to upgrade obsolete technology, especially when it is safety related. I would recommend you get yourself a more modern Depth / Speed or forward projection / side scanning sonar and head and transducer(s). Upgrading safety equipment is never a mistake. It keeps people alive.

If you choose to stick with what you have, maybe I am not seeing it right, but doesn't look to me like you need a whole scale hull repair. Looks to me that someone crafted and fared / shaped a block to fit the transducer and reduce drag. Also appears that what they built used several pieces of wood (laminated together to give the required depth), and only the outer / lower piece has failed based on what has chunked away. I don't see a fundamental fiberglass / hull failure issue here.

From the pictures, it looks to me like the block was constructed by cutting several pieces out of a piece of (hopefully) hardwood, drilling a hole to fit the transducer in each, and then laminating or screwing them together to build a hydrodynamic and protective block to house the transducer (less resistance when running, and haulout straps on the wood don't crush the transducer). My father's '69 Trojan had a depth transducer set up in a similar way - a 'torpedo' styled block was mounted under the hull to protect the transducer and make sure it pointed in the right direction.

In the pictures, it appears to me that the lowest laminated piece is screwed into the next piece, and (where the lower chunks of wood are gone) the next piece seems to have a very flat surface - so seems more likely a laminated situation than a block of wood that just split TOTALLY HORIZONTALLY.

Could you pull the screws, push, pry or chisel the lowest level piece of wood (laminate) off, and just replace it with a new piece of oak or ??? cut and shaped in the right depth, with appropriate hole size cut in the middle for the transducer, epoxied and screwed in to existing block?

New instrumentation would be my recommendation, but failing that I think you just need to replace this piece of the 'torpedo' encompassing the sensor, not redo the entire thru-hull fitting, because the rest looks intact.

May be dead wrong, but that's what I see.
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prowlersfish
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Re: Fiberglass Thru Hall Repair

Post by prowlersfish »

Tgornik wrote: Mon May 01, 2023 12:10 pm

Thought of this but would still have to mess with the diameter of the hole so just decided to plug and start over..

Thanks again.
Tg
If going to a transducer that is larger thread and nut I plug the hole by epoxy in a piece of wood so center the hole saws bit. Makes it easier
Boating is good for the soul
77/78 TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
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BobCT
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Re: Fiberglass Thru Hall Repair

Post by BobCT »

agreed, I wouldn't fill the hole only to re-drill it larger. That's a lot of work. I would use a piece of thin piece of plywood and screw it on the inside of the boat and use that to redrill new hole.
1988 10m mid cabin
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