Screwing into solid fiberglass

[Uncle Bob]

Originally Posted by Cheechako

If you actually mean the hull of the boat,... NO.
If you are talking a fiberglass part of the boat that doesn't contact the water on the other side of the fiberglass then drill and tap for a machine screw.
While you could use a blind tap and thread maybe 1/2" into the hull and find screws of a perfect length... I just wouldn't do that'
Make a wood or metal adaptor plate and glass that to the hull , then screw into that.

See Jims quote below.

Originally Posted by Jim Cate

Hey guys, he said "external" strainer, so the screws are from the outside of the hull, and there are no significant loads on the strainer. Likely won't be removed/reinstalled often, so I'd likely drill and tap for 10-24 screws (blind holes,of course... don't go through!).

But truth is that I'm not a fan of external strainers for cooling water... just another place to get growth fouling the flow, so OP, are you sure you want to do this? There have been some previous discussions here on CF, and a search will find a lot of chat about the use of strainers.

Jim

Agree with Jim, it will have to be removed to clean and antifoul every couple of years.

[finefurn]

Many Thanks to all. All the advice is very much appreciated. I see that I should have been a bit more clear on what I wanted to do and the circumstances that led to that decision. What had been on the boat for many years was a scoop style strainer. ( attached is a pic of what I had. ) While bottom painting the boat last year, I noticed barnacles growing inside the strainer. Which are a PITA to clear out. BTW ( marinehowto.com ) has an excellent thread on strainers and engine overheating. So I decided to cut off the strainer portion of the scoop style thru-hull and rely solely on the inboard strainer basket to filter the sea water. I have a 90 degree elbow attached to the thru hull before the shutoff. Over the course of the summer that elbow plugged twice with sea weed and once with a plastic bag causing the engine to overheat each time. So I figured this year the solution would be to add an external strainer that can be easily opened to clean ( see attached pic ) and change out the 90 degree elbow to either a 90 degrees sweep elbow or two 45 degree street elbows. All of the 90 sweep elbows I have found have a hose connection on one end. Are there any issues with having a short run of hose before the shutoff ?

[a64pilot]

All my strainers are the one you picture on the bottom, the round one. With only a few exceptions, I don’t believe scoop strainers ought to be on a sailboat, especially the engine, and while they may not hurt on the heads etc, they are not needed either.
When you do a bottom job, be sure to open them up, clean them out and anti-foul the inside, then nothing grows on the inside.

However I only plan on sailing in warm water, where there is no dangerous sea life, so diving on them isn’t a big deal, but if it were, then I would suggest to only glue them on so that they can be knocked off if necessary from the inside.
It’s my understanding that there are places in Australia for example that you don’t get into the water with the big Salties, and I would not get into 40f water willingly either.

[HopCar]

Originally Posted by a64pilot

However I only plan on sailing in warm water, where there is no dangerous sea life, so diving on them isn’t a big deal, but if it were, then I would suggest to only glue them on so that they can be knocked off if necessary from the inside.
It’s my understanding that there are places in Australia for example that you don’t get into the water with the big Salties, and I would not get into 40f water willingly either.

Instead of just glueing them on so they can be knocked off, I’ve thought it might be a good idea to just use a weak pin to hold them closed. That way you could bang on them from inside and shear the pin. This would allow you to open them without losing an expensive fitting.

[a64pilot]

Originally Posted by HopCar

Instead of just glueing them on so they can be knocked off, I’ve thought it might be a good idea to just use a weak pin to hold them closed. That way you could bang on them from inside and shear the pin. This would allow you to open them without losing an expensive fitting.

That would work, but to be truthful, just closing the thing, it will stay closed all on its own, no pin needed, or mine do anyway.
Somehow I broke mine off of the engine intake trying to open it underwater, I was prying up on the pin I thought, but likely was prying on the cover too.
I’m leaving it off, won’t likely replace it. The one for my Watermaker I had the pin out and it stayed closed on its own.

[thinwater]

I've had the Marlon/Forespar sort on my AC intake. It did a GREAT job of preventing minnows, jellyfish, and spartina from clogging the inlet. Without it, in some harbor the intake could clog within minutes. In others, a fish would get caught in a bend, requiring disassembly. Ugh.


Cleaning? About 2-3x per year I would spend a few minutes with a small screwdriver, ordinarily when I was swimming anyway. Other inlets needed a little cleaning as well and I like to look over the bottom and prop a few times each season anyway. It just not the big deal some make out. It just isn't. And yes, I keep the boat in the water and we get ice every year. Not much grows in the cold, and if you are a cold water sailor, having either a wet suit or dry suit and knowing how to use it is just basic seamanship.



I'm sure it depends on the inlet function and the local area. I did not have them on all inlets and did not want them; it was only needed on the AC inlet. If you don't have AC or a gen set (something that draws while the boat is motionless) there is probably no need.

[Whisper 2]

It's SELF TAPPERS!

[Estica]

Pilot holes for your short wood screws will work - but first take down bottom paint and apply 4200 or 5200 to the edge of the strainer. Small job and it’ll hold forever.

BUT I agree with others - I wouldn’t do it at all. I have a strainer over my low flow generator intake but not over my high flow engine intake.

[Boater Brad]

Originally Posted by Estica

Pilot holes for your short wood screws will work...

Not sure if you meant this, but don't use wood screws--they are tapered and you can't create a proper pilot hole. I, too, have a solid fiberglass hull and a pilot hole that is too small can easily make the screw nearly impossible to screw in and may--heaven forbid--snap off. The pilot hole only needs to be slightly smaller for the screw to grab tenaciously. I'm also not a fan of drilling oversized holes then wrestling with refilling with resin and tapping--especially upside down. That's overkill and too much damage. And 5200 is not impossible to remove (it can be a p.i.t.a., but anyone who has really worked on boats has done it many times).

[Estica]

Yup, short wood screws to affix the strainer to the hull while the 5200 sets. And of course as with all glass jobs squirt 4200 into the screw holes before putting in the screws. Just tellin’ you what I’ve done and has worked. A good commissioning and sailing season to all!

[Boater Brad]

Originally Posted by Estica

Yup, short wood screws...

I think this is a mistake. Wood screws are for wood. Their taper is intended to act as a wedge and exert increased pressure as the screw is being driven into wood--which is an elastic material. Fiberglass and resin are not elastic, so a tapered screw is not appropriate. If you drill a smaller pilot hole sized towards the skinny end of the screw, you won't be able to drive it home and it will strip or snap. If you drill a pilot hole sized to the larger part of the wood screw, you are wasting the gripping power of the skinny end of the screw. Also, wood screws are not threaded all the way to the head which is required in this application. A "sheet metal" or a straight tapered self tapping screw is correct here. Wood screws have no place attaching anything to fiberglass.

[Estica]

Right you are. My mistake. short sheet metal screws threaded right to the top is what I used. Works fine in non “critical strength “ applications attaching things to glass.