Rebedding a through-hull

kmart

.
Jan 1, 2012
87
Pearson 10M Fall River, MA
OK, now I am really worried. I was initially surprised when I saw the gasket.
And it was remarkably secure. before freeing up, i did put my weight on it from the inside and it didn't budge.
And I thought the old through-hull looked pretty good. I didn't see the gouges in the flange until you pointed them out in the picture. They are not as obvious looking at it as it is in the picture.
Gasket is rubber-ish. Its looks like the standard gasket that came with the transducer but meant for the inside under the lock ring.

So I guess my options are:
1) find a new throughhull that matches my existing transducer (Maine Sail.. could you point me to a sorce for this?)
2) get an entire new transducer including new throughull
3) put in a new throughout with sea-cock just to close off the hole... and no transducer
4) permanently close the hole and not have a knot transducer.

I'm still not clear on how / what to modify the hole?
Are you saying the entire flange need to sit flush on the surface of the hull to seal properly?
That certainly was not the case with the old one. And where its located. And based on where its located That would be difficult to do with the concave curvature of the hull at that point.

While not my preference, I can certainly live with out a knot-meter since mostly rely on GPS speed anyways. (Yet I know its not the same thing!) Does autopilot (EV 100) use knot speed when sailing be the wind?
I'm getting a quote from my yard now for the options. Leaning between options 2 & 4 as fastest, cheapest and safest solution.

So much for the easy, cheap do it yourself maint. And I thought I launch early this year :-( Grrrrrrr
 
May 20, 2016
3,015
Catalina 36 MK1 94 Everett, WA
I installed depth and speed transducers that had that profile back in 1984. I don't remember the brand (signet??). I had to rent a special bit to make the hole.

I looked on airmar's web site and only saw mushroom head. You might ask some one more knowable than me if you can convert the chamfer into a "pocket" to flush mount the mushroom. And if youwould need to reenforce the back to makeup for reduced hull thickness.
 
Jan 11, 2014
13,009
Sabre 362 113 Fair Haven, NY
SR Mariner was one of the brands that used the recessed flanged. I remember trying to grind out the flange well enough to bed the transducer. I think it is still working some 30+ years later (I don't own the boat anymore, but it is in my marina, I'll check it out.)

Newer transducers and through hulls have a flap that blocks water when the transducer is removed for cleaning. That alone is worth the upgrade.

If going with a new transducer, the question is the hole size. If the hole is bigger than the current hole, there may be a lot less work as the bevel will be smaller and easier to fill. If it is smaller that's a bigger job.
 

kmart

.
Jan 1, 2012
87
Pearson 10M Fall River, MA
So as I have RAYMARINE instruments. I quick search and I found Raymarine ST800/P120 Low Profile Retractable Thru-Hull Transducer. Comparable with my system. About $65 or so. (could be worse). Specs says it needs a 2" hole. which is the same size as the current through hull. So it will fit.. but its still the mushroom type head. So I have the same problem trying to fit it without fiberglass work and deal with the taper..

So would the idea be to eliminate the taper in he hole and at same time make a flat surface for the flange to sit on? I've done simple fiberglass work but I'm not up to that. not even sure how to do it?
 

kmart

.
Jan 1, 2012
87
Pearson 10M Fall River, MA
So I know its my boat, my risk, my choice.
But the old one was there for the 9 years I've owned the boat... and I'm sure it had been there long before I bought it (I'm guessing another 10 years prior to me). And it was in and still very strong before I removed it. Even without lock nut... my weight on inside it didn't budge it to push out. And there is no way it could push up through into the hull.

So beyond doing it the right way (which is my preference) What is the real risk of remounting (a new one) similar to the way the old one was mounted? That's a rhetorical question.. No one should really answer that without actually inspecting the boat themselves.. Just mussing aloud on how I can reasonable and still safely get this fixed. I should've looked at this in the fall when I hauled out!!!!! Uggg!
 
Jan 11, 2014
13,009
Sabre 362 113 Fair Haven, NY
If the new transducer is going to fit in the hole, what you need to do is bring the bevel up to the hull. This is not a big issue. First clean and sand an area around the hole. and clean all of the old bedding compound out of the bevel and hole. A dremel tool will help with this.

Once every thing is cleaned up, fill the bevel with thickened epoxy and bring it close to the surface. Clean it up so the transducer fits. Install the transducer with an appropriate bedding compound. If you follow this route the hull will be no weaker than it is now.

The really proper solution is to grind the area out to get a 12:1 taper, lay up glass and epoxy to make the hull fair and then drill the hole to fit the transducer. What you are doing here is rebuilding the hull and then drilling the hole.
 

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,253
CAL 35 Cruiser #21 moored EVERETT WA
It is your boat and your decision for you and all who may join you in your water adventures. :biggrin:
You know what the answer is. :banghead:
We want you back here for many years to come so we can share in your joy and misery:deadhorse: like the rest of us.

The filling of a hole is not rocket science but it does require you to follow the recommended procedures.

Try this link... http://www.westsystem.com/ss/repairing-machined-holes-in-fiberglass/

Look down at the section "Zone 3-High-risk repairs requiring additional reinforcing" That is the type of hole you have.

You can use my friend "Google":laugh: to get videos about this type of repair.
Or you can look to a boat yard for help. :kick:
This has been done before by many boaters not as discerning as you..
You got this.:cool:
 
Jun 21, 2004
2,920
Beneteau 343 Slidell, LA
If you decide to close the hole and do without the knotmeter, follow John's advice with the West Systems instructions.
If you are going to replace the transducer / thru hull fitting with the same diameter thruhull, clean up the exterior of the hull and get down to a clean gelcoat surface; also clean up the lateral surfaces of the hole thoroughly and cut some horizontal undercuts in the sides of the hole using a separating disc on your dremel. Wash all surfaces thoroughly with acetone. Apply tape to the bottom of the hull and fill up the hole from the inside with thickened epoxy about 3/4 up to the top of the hole on the inside surface of the hull (make sure the epoxy goes into the undercuts that you prepped in the sides of the hole). After it cures, remove the tape from the hull and wash with acetone again. Add two lightweight fiberglass cloth layups over the repair on the outside of the hull, the last layup overlapping the first layup. After it cures thoroughly, redrill the hole from inside the boat. Remember, you only filled the hole about 3/4 so you should have a good shoulder remaining to guide your hole saw on the drill. You can buy the appropriate size hole saw at Home Depot inexpensively. After, the hole is drilled, fair the outside of the hull where you applied the layups so that your mushroom flange will fit flush to the hull. Rebed with 3M 4200 or appropriate sealant recommended by the transducer manufacturer and you should be good. I know that it is tempting to place a bunch of sealant as the previous owner did; however, I don't think it is safe to go that route again. This repair should not be too difficult; however, its going to take a bit of time doing the glass work. Might want to use a flood light or reflector lamp to accelerate the curing of the epoxy if the ambient temps aren't cooperating. With the mechanical undercuts in the sides of the hole, bonding to the inside of the hole, and a couple of cloth layups on the outside of the hull, the repair should be more than adequate.
 

kmart

.
Jan 1, 2012
87
Pearson 10M Fall River, MA
So I was initially overthinking this and how to patch this...thus my worry.
But will all your advise, I see this a very doable. I usually have no concerns diving into DIY projects. Worst I can do is screw it up :) except when it comes to things that cans sink the boat!

So I'm going to go with replacing the through hull/ transducer. Unless I can find just the throug-hull that matches the existing transducer. But that's same repair either way.

I'll follow the above instructions to clean, then fill in existing hole 3/4 of the way with west system .
Put 1 -2 layers of cloth on outside of hull. (expanding and cleaning te area on the hull
Should these be weave or chop mat? I have some of both
Fair, Drill new hole.
Then properly bed the new through-hull,

When filling the hole "Tape outside of hole to fill" What tape do I use that won't become infused with resin and thus impossible to remove later??

My other question is the "undercuts in the sides of hole".
So am i just cutting small horizontal slots in the vertical sides of the hole for the resin to fill in and bite.
or cut in more like steps. ( much harder.)
Some sort of rough sketch will help me visualize the undercuts better.

When all done and said.. I'm really just filling in the bevel in the hole... which is a really small area. 1/4 - 1/2 inch
 

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,253
CAL 35 Cruiser #21 moored EVERETT WA
Kmart
Reading your last post gave me pause. You have a hole beneath the waterline. You need to restore the outer hull integrity. The issue with resin and fiberglass is to create strength and attachment to the existing surface.
I would use the suggested grinding - widening of the outside hole to 12:1 bevel. Then use the layer woven method to bring the level of the hole back to the level of the hull. This often means 7 or more layers of cloth in progressively larger circles to rebuild the hull, establishing hull strength to the hole. Once rebuilt back to the hull level and properly cured the patch will be as strong as the rest of the hull. Then if you want a new hole in the same place drill the new hole. The area outside of the new hole but in the area of the repair will be the same strength as any other location in the hull.

The first process of rebuilding the strength to a hole is to establish enough physical strength to the issue. The second is to establish a proper chemical bond to the underlying structure.
The chopped mat and resin approach misses the physical strength portion of this rebuild.
 
Jan 11, 2014
13,009
Sabre 362 113 Fair Haven, NY
Don't over think this.

If you are going to replace the through hull and transducer in the same location there is no need to grind out to 12:1 glass everything up and and drill a new hole. This is a way to reduce the hole diameter or fill in the bevel to fit a new transducer, it is not the way to permanently plug the hole.

If the new transducer is the same or larger diameter all that needs to be done is to fill the beveled area to be fair with the hull. The beveled area needs to be very clean, i.e. all of the older caulk needs to be gone and as well as any contaminants. Then fill it with thickened epoxy. Epoxy is a better choice than polyester because it has better adhesion properties than polyester and is less likely to shrink over time. To add structural strength to the epoxy, cut up some fiberglass fibers in to ¼" lengths and mix it into the epoxy. Once it is cured, drill the hole out to the proper size, clean up the area and fair as necessary. And be done.

The reason this works is that it is a very small area that is being built up, the presence of the through hull fitting and the compression of the through hull fitting helps to strengthen the area. In the end, the hull thickness will be greater than it was with the original transducer installed and the epoxy is stronger than the plastic through hull.
 

kmart

.
Jan 1, 2012
87
Pearson 10M Fall River, MA
Jssailem, If I was going to fill the hole up entirely / permanently .... I would do exactly as you suggest with the 12:1 multiple layup of glass. In fact doing that is what had me worried as its above my level of experience/comfort level. If I went that route.. I'll have my marina do the work.

BUT, that's not the route I intend to go. I'm doing what dlochner is suggesting.
I have an existing 2" clean hole in the hull. Except for the the last 1/4 of the outside of the hole
which is tapered from 2" to about 2.5"

Both the original, and the new replacement through hull are exactly 2" diameter.
I am neither enlarging or shrinking or closing the existing hole. I'm only filling in the small tapered area.
Also note the flange of the through-hull is 3" diameter so it extends beyond the tapered area to be filled in.
By filling the taper, the flange will fit flush with the hull along its entire surface. Unlike the old one that was improperly bedded. There was a gasket used to fill in the taper..

I planned on using west system epoxy. I'll add some fiberglass fibers in with the filler.

I will put tape on the outside of the hull over the hole. Fill the hole with resin to just above where the taper starts.
After it cures... Re drill out the bottom. Then ...no more taper, I'll have an even 2" diameter hole the entire length of the hole and a flat surface for the flange.
I will probably put 1 or two layers of cloth over the outside of the hull for piece of mind. (larger than original hole.) (Before drilling out the new hole. )

Last observation. This is a 1978 Pearson. Built like a tank, The fiberglass is very thick (I don't have exact measure) But its rock solid. Filling the tapers is to get the through-hull to seat properly. In this specific case, structural strength of the hull is not an issue as its already strong enough. As dlochner mentioned... "compression of the through hull fitting" ...it's not gonna move. and if I clean and bed it well ..it shouldn't leak either

Drawing1.jpg
 
Jun 21, 2004
2,920
Beneteau 343 Slidell, LA
Kmart,
You are on the right track now. As Dlochner pointed out, you already have a taper with the widest part on the outside of the hull. When you finish the repair, the flange on the new thru hull will be exerting an upward force into the hull and into the taper. Your epoxy repair can go nowhere except upwards into the taper---it isn't going to budge. Just clean it up good and wash it thoroughly with acetone to get a good bond. The slots are optional; however, if you do place them, think simple. You don't need "steps" just put a separating disc on your dremel and cut a few horizontal slots (4) into the sides of the hole approximately 1/4" to add some mechanical retention. The only reason I suggested two small cloth lay ups was to give a bit of added material on the outside of the hull to allow you to fair the bottom of the hull so that it is flat where the thru hull mushroom will fit on the exterior hull surface; you want a nice flat fit of the edges of the mushroom where it contacts the surface of the hull. You may not even need to add the layups if you can get a 3-4" flat perimeter on which to seat the mushroom. I wouldn't worry about the 12 to 1 ratio for layups because you are not attempting to close the hole permanently. If you do decide to add layups, make the first one about an inch wider than the widest diameter of the mushroom and the second one two inches wider. Again, these layups may not even be necessary. Good luck, let us know how it works out.
 

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,253
CAL 35 Cruiser #21 moored EVERETT WA
Sounds good. Make it fair so you get a solid flush fit when installing the thru hull,will help to assure a dry boat.
 

kmart

.
Jan 1, 2012
87
Pearson 10M Fall River, MA
Thanks everyone who provided advice.
I'll work on this project this weekend.
I'll report back on how it went and with pics.
Best
K
 

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,253
CAL 35 Cruiser #21 moored EVERETT WA
Good Luck... To error is Human, to have to do over is boat work.
 

kmart

.
Jan 1, 2012
87
Pearson 10M Fall River, MA
So, My update on my repairs so far:
1) using a scraper..removed all the old 5200
2) used a dermal tool with sanding drum sand the surface down.
3) cleaned up with acetone
20170413_121015.jpg

So next the plan was to cover the hole with tape so I could fill in the hole with resin.
BUT... I was worried the resin would just leak out. as well as infuse the tape...thus making it impossible to remove.
Also, the surface would not be anywhere near flat or fair and would reuire a lot of work to make it so.

My solution was to cut a round, flat disk out of a small piece of wood, slightly larger than the flange on the through hull.
Covered this with wax paper. Now because the hull is concave at the location of the hull ...it wont sit flat over the hole.
I used some window sealant (a kind of putty). to build up the sides and hold the disk in place.
20170413_151301.jpg

Poured resin (West System ) in the hole from inside.
After it cured, removed wood disk and I have a nice filled/plugged hole.
20170413_162055.jpg
 

kmart

.
Jan 1, 2012
87
Pearson 10M Fall River, MA
Part #2
Drilled out hole from inside using original boarder as a guide. 2" hole saw
20170414_114941.jpg


You can see where the bevel was filled in.
Also because of the disk that was used when filling the hole. The outside surface is flat and even ...exaclty matching the flange on the through hull. in the pic it lookd rough but its actually quite smooth and level. I cleaned up the edges post this pic
20170418_134819.jpg


I used 4200 as sealant. This is picture after installed

And from the outside.
OK.. I know its a mess. I was overly generous applying the 4200. Then when I tightened the inside lock nut, it squeezed out everywhere. Trying to fair it out...made a even bigger mess.
I'll clean it up best I can after it cures... But I'm sure she aint gonna leak.

Note, per the instructions, the sealant is not just under the flange but also fills in the gap between hole and through hull sides.. all the way up to and under the locking nut.


20170418_141936.jpg



I was also able to snake the transducer cable under the sole, behind the cabinets, behind the hull liner all the way to the back of the knot-meter Autohelm st50 gauge.

Last step will be to wire it in and test. The knot meter cable has 5 wires (Red, Yellow, Blue, Green and bare).
The back of the gauge has the very old ( sea talk round) connector. ( I think it also uses 5 wires) I plan to cut of the connector of the old existing cable and wire it into the end of the new cable... And reuse the existing connector to the gauge. Hopefully it has the same color coding.

Hopefully my next report will be that all is working!
And thanks again for all those who advised me on this.
Best
Ken
 
Jun 21, 2004
2,920
Beneteau 343 Slidell, LA
Looks good Ken. No more leaks!!!
After all of the 4200 dries completely, use a utility blade or exacto knife to cut thru the sealer around the perimeter of the thru hull. Use a razor type scraper on the hull and a bit of solvent on the thru hull flange ---should clean up nicely.