Chain Plate Slot Cutting

[ShipShape]

My inner forestay chain plate leaked terribly and rotted much of the bulkhead to which it was bolted, as well as the deck core through which it penetrated. I have re-built the bulkhead with epoxy and fiberglass, removed most of the rotten deck core and filled the space with epoxy, and built up the underside of the deck with epoxied marine plywood - which matters because the L-shaped chain plate is also bolted through the deck.

Now it is time to install the new, much larger, chain plate. I would prefer to cut the slot with a multi-tool, starting the forward cut by sliding the blade straight up the bulkhead to the deck ... but with all my reinforcing the deck thickness is now 2.5 inches and the longest blades I have found are 2 inches.

The scar from the original slot is still partially visible on deck, but 1) it was a sloppy, wiggly POS hole, 2) it did not line up with the bulkhead - it was too far aft, and 3) my new chain plate is more than 1.5x larger than the warped original one. The project is further complicated because the bow of my boat has a phenomenal amount of camber as well as slope aft, plus he lists to starboard a lot since all my tools are on that side.

Any ideas how to cut a NEAT, tight-fitting hole for the new chain plate? It is 3/8" thick, 3" wide, and the deck is now 2.5" thick where it will penetrate. (I have both the Harbor Freight $49.95 multi-tool and the Bosch multi-tool if you know of 2.5"-long blades that will fit either of these tools.)

For anybody who suggests something sloppy, such as drilling a row of 3/8" holes through the deck - you will get a nasty rash in a bad place.

[perchance]

A Sawzall with appropriate blade?

[Cheechako]

I think you're too enamoured with your new tools. :>) 3/8 hole at each end, saw hole to hole. File to fit. Arent you going to need to get in there to seal the exposed core when you cut anyway?? and a question for the group: Can a hole like this be too tight fitting, thuse not allowing enough sealant?

[daddle]

How much gap for sealant is a good question. I'd say the water should stop at the deck level. The underside open to the air. A tight fitting s/s deck plate should be part of the assembly. Sealant under it only.

As far as making the slot...yes...a row of neatly drilled holes then chiseled out...this is how a shipwright would do it...but then maybe you've watched too many hours of TV woodshop shows and fancy things like this have always been done in seconds with $200 power tools.

Thanks for the painful rash offer, already got one.

[barnakiel]

It is OK for the gap to be relatively tight if the fitting is pre-bent to an exact angle. The sealant can be then applied into the slots, pre-fitting. Afterwards, a lip is built round the plate and filled high with appropriate type of sika-thing. Such a sika-seal will be thick enough to allow for any slight movement of the fitting. No leaks ever. It has to be replaced every 3-5 years depending on how hard the boat is used and how much sun & seawater it receives.

b.

[ShipShape]

perchance - I LOVE my sawsall - it is more fun and useful than any man who has ever been in my life, and I probably have every blade available. Wanna prevent a bad rash and tell me how to get the sawsall flush with the bulkhead AND penetrate the deck with it? (Thank goodness sex isn't so challenging )

Cheechako - my tools are not new, and I am enamored with skill and intelligence, not cheap crap manufactured in China. Can you tell me how to drill two vertical 3/8" holes in my deck exactly aft of the bulkhead, what saw blade will fit one of those holes, and what tool will cut a STRAIGHT cut to the next hole? Exposed core?? It is gone Hon, if you read my post it was rotten - I dug it out and filled the space with epoxy.

daddle - I have never owned a TV and never will. You are correct, water should (must) stop at deck level. There are several places in my boat with chiseled out drilled holes - sloppy sh!t - that is why you have a rash. This hole is important, do you know of a $200 tool that will do the job??? (I guess you don't want me to sign your rash, eh? , and I ain't gonna kiss it )

barnakiel - butyl rubber tape 'never' has to be replaced. but don't just take MY word for it, see: Re-Bedding Deck Hardware Photo Gallery by Compass Marine at pbase.com

[minaret]

LOL!! I already have a rash, but let me suggest a pneumatic file. If you really want perfection start the cut with a Kettsaw and finish it with the file. Show me a pro who would chisel fiberglass and I'll show you a liar.

[daddle]

Yes, if you chisel a sloppy hole you will have a sloppy hole. I would drill perfect holes with a perfectly sharp bit. And chisel it out. A SawsAll is a good way too but you may want to take precautions to avoid marring the bulkhead. Cut very slowly to keep it square (not simple in thick plywood) and shim the saw up so the blade just penetrates. Finding where to put the first cut is a problem for all the methods that start from the deck side. Simple: Drill a very small hole, or two, anywhere nearby and measure from there. Patch the small hole later. I thought the deck was plywood with maybe fiberglass on the outside. Fiberglass chisels okay ... for a pro and a sharp chisel. Actually, I would have considered the slot before starting all the repair work. Building around a dummy plate would have been clever.

[Cheechako]

Cheechako - my tools are not new, and I am enamored with skill and intelligence, not cheap crap manufactured in China. Can you tell me how to drill two vertical 3/8" holes in my deck exactly aft of the bulkhead, what saw blade will fit one of those holes, and what tool will cut a STRAIGHT cut to the next hole? Exposed core?? It is gone Hon, if you read my post it was rotten - I dug it out and filled the space with epoxy.
Just kidding about the tools!
I believe you indicated you can (pretty much) tell where the old slot was. I would probably drill a small hole in the middle of where that is.
(1/8" or less) Then go below and measure how far from the bulkhead that little hole is. Make adjustments accordingly, layout the slot, maybe even outline it with masking tape. Then drill two small holes at the center mark where you are going to put the two 3/8 holes eventually. Check below again that these two are the correct distance from the bulkhead. Then drill the 3/8 holes (or a littel smaller if you want) The use a big bastard file and file to the line. The file will square up the ends of the 3/8 holes if you want also. "measure twice cut once". Surely you can eyeball the drill to be perpindicular to the water...? Or buy yourself a drill with the bubble level on it.... Let's face it, that slot should be covered with a sealant fillet when you are done anyway...
what tool will cut a STRAIGHT cut to the next hole? YOU are the tool that can or cant do that....

[Vamonos]

Here is a long reach blade that will fit Bosch multi-tool...It says 2 5/8" long. Hopefully that is all usable length.

[minaret]

Don't forget for non-reciprocating saws hot gluing a batten to the work surface as a guide will give you dead straight cuts every time. You can also do the same with a router for most of the cut and finish off the ends/bottom of the cut by other means.
I would find the bulkhead by taking a pic with our 20k dollar thermal imaging cam, but I doubt that's an option for most. How's that for expensive toys? Failing that anyone who's good at sounding can tell you where it is to within an inch. From there you find center athwartships and drill a hole. If its not perfectly located it will get cut out with the rest of the slot.

[brankin]

here is a simple solution. Plunge cut as deep as you can on all sides of the slot. This will create a box with a small amount of glass to remove from the top. Now plunge cut at an angle so you are removing material from the center. Remove as much of the material from the inside as you can by any means you can. IE die grinder with carbide tip. Drill a hole as close to the center of the slot as possible. Then enlarge the hole to allow for a straight cut 1/4" router bit with a bottom bearing . Set the depth of the bearing just below the bottom of the remaining material that needs to be removed. The bearing will follow the edge made by the vertical plunge cut and you will have a perfect rectangular hole with small curves in the corner that you can trim with a file.

[minaret]

Originally Posted by brankin

here is a simple solution. Plunge cut as deep as you can on all sides of the slot. This will create a box with a small amount of glass to remove from the top. Now plunge cut at an angle so you are removing material from the center. Remove as much of the material from the inside as you can by any means you can. IE die grinder with carbide tip. Drill a hole as close to the center of the slot as possible. Then enlarge the hole to allow for a straight cut 1/4" router bit with a bottom bearing . Set the depth of the bearing just below the bottom of the remaining material that needs to be removed. The bearing will follow the edge made by the vertical plunge cut and you will have a perfect rectangular hole with small curves in the corner that you can trim with a file.

The problem with this technique is that the ends of the slot will need to be an angle other than square to the deck, which a router cannot do without a jig. That's why I recommended doing the center of the slot with a router and finishing the ends of the cut by other means, ie drilling at the exact angle needed and finishing by hand. A rasp is much better than a file for that, files dont do too hot on glass except for the final bit. Of course it doesn't need to be that perfect, the underside of the slot doesn't really matter and so it could be done as you suggest with some extra rasp work on the ends and noone would be the wiser except the person who did the job. However, the OP asked for tools and methods to acheive perfection in fit. A router is almost always best for this. If you build a jig you can make a perfect cut, angles and all, but that's just overkill, even to me.

[ShipShape]

Vamonos - if you posted a link it did not go thru, but I googled your phrase and came up with multitoolblade.com - Sweet! I have already placed an order. I'll start the cuts with a short blade since it will be stiffer, and finish the last half-inch with the long-reach one.

minaret - you must have such a fun life! Hadn't heard of kettsaws before, intersting tool! The idea of a pneumatic file reminded me that recently I saw sawzall accessories on McMaster-Carr, and one of them is a file. I see there is also a flush-cut adapter. Gosh, that is such a powerful tool I think the flush-cut adapter would be a little dangerous, and I would still need to get a cut through the entire deck to use it. Good info to keep in mind for future projects.

There are a lot of problems/issues with going through the deck side, it *can* be done, but since I can't use a level or square it would be a series of trials and errors that would take time to straighten up. The original slot was sloppy, in the wrong position, and now that I decided to upgrade the chain plate, too small. From inside it is easy to find the center of the bulkhead, as well as the perpendicular to the deck.

So, my plan is this:
Cut the center 1.5" - 2" of the slot flush to the bulkhead.
Place a 3/8" spacer against the bulkhead to simulate the thickness of the chain place and make the same cut again.
Now I have two parallel cuts on deck and can find the center.
Mark the cuts out for the 3" width, drill a 3/8" hole on each end, and finish cutting the remainder of the slot.

The saw blades should arrive in two to three days, I'll let everyone know how it goes and post a pic.

THANK YOU to everyone for all your help and ideas.

[minaret]

Originally Posted by ShipShape

minaret - you must have such a fun life! Hadn't heard of kettsaws before, intersting tool! The idea of a pneumatic file reminded me that recently I saw sawzall accessories on McMaster-Carr, and one of them is a file. I see there is also a flush-cut adapter. Gosh, that is such a powerful tool I think the flush-cut adapter would be a little dangerous, and I would still need to get a cut through the entire deck to use it. Good info to keep in mind for future projects.

Just so you know, a pneumatic file is not a "file" per se, it is essentially a tiny air powered sawzall, though you can chuck in files and that was the original purpose. It uses hacksaw or sawzall blades, which means you can break a hacksaw blade off to the exact length you need or use a sawzall blade of your choice if you need a stiffer blade. Since it's so much smaller than a sawzall you can use it in tight places and get right up to bulkheads and the like. Also has much more control than a sawzall-great for boat surgery. There can be a lot of confusion in google searching because a "hustler" or body file is also often described as a pneumatic file and is a much more common tool. Things like that are common when you start getting into really obscure tools.