Cutting out a bulkhead

[12 metre]

Any tips, tools, or tricks to expedite the removal of some partial bulkheads?

I've cut the majority out (down to just above the tabbing) using an Ultra-Saw, which is quick and easy for cutting straight lines in up to 3/4" plywood.

Problem now is cutting out the remaining stub portions that are still tabbed to the hull - so about 2-3" stubs

I've used an oscillating tool with a semi-circular blade that gets to within about 1/2" or so.  The remainder can be ground out.  

But the oscillating tool is painfully slow because:

1) it does not cut through fiberglass as well as it does plywood, and

2) I have to make a series of perpendicular and straight parallel cuts (since the semi-circular blades only cut straight and can't follow the curve of the bilge).  Basically taking it out in 3-4" wide pieces.

In an attempt to speed thing ups, I stupidly bought a Rotozip (which I will likely return) figuring that would work, but the bits mainly just burn the plywood

One thing that may work is either a Rotozip or Ultra-Saw wood cutting wheel attached to a grinder if they will fit - I haven't checked.  Both wheels are good up to 15,000 rpm or so

So, is there a better way? Or should I resign myself to spending way more time than I would like removing the bulkheads?

 

[Diarmuid]

Hmmm. I find multitools zip right thru FRP, much faster than thru wood or wood composites; and the blade teeth seem to last forever on FRP for some reason. While the urea or resorcenol glues in any panel product will blunt them quickly.  Multitool with a medium wood/metal blade is my go-to for cutting tabbing, opening deck skins or cabin soles, etc. Multitools are a bit slow, but three passes or so usually does the trick. Gotta hold them at the right angle -- 45 degrees or so on a plunge cutting blade seems to work best.

 

[12 metre]

Hmmm. I find multitools zip right thru FRP, much faster than thru wood or wood composites; and the blade teeth seem to last forever on FRP for some reason. While the urea or resorcenol glues in any panel product will blunt them quickly.  Multitool with a medium wood/metal blade is my go-to for cutting tabbing, opening deck skins or cabin soles, etc. Multitools are a bit slow, but three passes or so usually does the trick. Gotta hold them at the right angle -- 45 degrees or so on a plunge cutting blade seems to work best.

Interesting.   I am able to zip through the bare plywood portions at a reasonable speed but find it slows right down when cutting into the tabbed portions.

Perhaps I'm using the wrong blade?  I've been using a semi-circular blade since it looks to have a longer cutting edge than a plunge cut blade.  Maybe time to invest in a decent plunge cut blade (the ones that came with the tool were useless and the teeth wore down within a couple of minutes of use.  Is it safe to assume a plunge cut blade will also allow curved cutting to follow the line of the bilge? 

 

[Diarmuid]

Don't waste $$ on good blades.  Harbor Freight has perfectly decent universal blades for $6-9. I find the half moon blades useful for cutting long runs of drywall, but that's about all.  Harder to get the aggressive, forward-pointing angle you need for zipping thru FRP. These are the puppies I use:

https://www.harborfreight.com/1-38-in-High-Carbon-Steel-Multi-Tool-Plunge-Blade-61816.html

https://www.harborfreight.com/1-18-in-bi-metal-multi-tool-plunge-blade-61812.html

I've cut hundreds of feet of fiberglass with them, including tabbing over 1/4" thick.. You can turn a tight and neat corner, no problem. Honestly, you try to cut 3" of MDF with these tools & and the blade starts burning & the teeth wear down to zero. But I've been using the same blade on FRP for, like, months, and it still looks & cuts fine. 

I make the first pass with the teeth almost parallel to the surface, to make a scribe cut.  Second pass at maybe a 15-30 degree angle, removing ~half the material. Third pass usually plunges thru the material & then I cut using the center of the blade, with the teeth at maybe 45 degrees to the surface.  This is a really powerful &satisfying pass. 

 

[12 metre]

Thanks for the assistance.  It's a it of a pain to get stuff into Canada from Harbor Freight, but I'll look for something similar at CT

 

[Diarmuid]

Thanks for the assistance.  It's a it of a pain to get stuff into Canada from Harbor Freight, but I'll look for something similar at CT

Here ya go:

http://www.canadiantire.ca/en/pdp/mastercraft-1-1-4-in-wood-and-metal-flush-cut-blade-0545506p.html#srp

Twofer.

 

[12 metre]

Here ya go:

http://www.canadiantire.ca/en/pdp/mastercraft-1-1-4-in-wood-and-metal-flush-cut-blade-0545506p.html#srp

Twofer.

Even the Harbor Freight ones are better than those.  Those are the ones I mentioned that wore out in a couple of minutes.  When I said "invest in a decent plunge cut blade", I didn't necessarily mean pricey, I meant bi-metal like the second Harbor Freight ones you listed.  I think there are titanium tipped ones (or something like that) available at CT for not a whole bunch more money.

 

[Rain Man]

Assuming this is the Dash, the easiest way to get a bulkhead out is to attack the tabbing.  Get a chisel head underneath the tabbing and you'll discover it strips right off the underlying laminate.  After you discover how easy it is to strip the tabbing, you'll consider using epoxy the next time you tab in a bulkhead.

Take off one side of the tabbing, pull the bulkhead remnants off, then go at the rest of the tabbing from that side.  

You should be able to get the forward bulkhead out of the Dash in 3-4 hours, if I recall correctly how long it took me (once the forward floor and side locker had been removed).  As a bonus, with this method your boat won't be full of fibreglass dust.

 

[12 metre]

Assuming this is the Dash, the easiest way to get a bulkhead out is to attack the tabbing.  Get a chisel head underneath the tabbing and you'll discover it strips right off the underlying laminate.  After you discover how easy it is to strip the tabbing, you'll consider using epoxy the next time you tab in a bulkhead.

Take off one side of the tabbing, pull the bulkhead remnants off, then go at the rest of the tabbing from that side.  

You should be able to get the forward bulkhead out of the Dash in 3-4 hours, if I recall correctly how long it took me (once the forward floor and side locker had been removed).  As a bonus, with this method your boat won't be full of fibreglass dust.

The forward one will come out later after I`ve built the new one in the new location about 4 ft aft.  The forward one looks pretty easy to take out since it was bolted to the liner and that is gone now.

The ones I`m cutting out now are the partials one attached to the end of the settees.  I agree its pretty easy to chisel out the tabbing in places like under the deck at the deck to cabin joint - but I can`t find a place to start in the bilge or topside areas.

The process would probably be a lot easier if the plywood was rotten, but it`s only a bit punky along the bottom couple of inches. 

 

[waXrules]

I've had good luck buying oscillating saw blades from these guys.  They're located in Toronto and shipped the same day I ordered them online.

http://multitoolblades.ca/

 

[Rain Man]

The forward one will come out later after I`ve built the new one in the new location about 4 ft aft.  The forward one looks pretty easy to take out since it was bolted to the liner and that is gone now.

The ones I`m cutting out now are the partials one attached to the end of the settees.  I agree its pretty easy to chisel out the tabbing in places like under the deck at the deck to cabin joint - but I can`t find a place to start in the bilge or topside areas.

The process would probably be a lot easier if the plywood was rotten, but it`s only a bit punky along the bottom couple of inches. 

View attachment 240452

I removed my port settee using the method described.  In the photo you can see the edge of the tabbing in the near bulkhead - the sawdust is piled up against the edge. Put a sharp chisel against that edge, and a few hits should get a bit of it loose enough to start stripping it off.  You might have to probe a few spots to find a weakly bonded area - the chisel may just bounce on the gelcoat in some places, or it may only peel up a few layers instead of the whole tab.  Keep trying until you locate a spot where the whole tab can be separated.

Once you get a bit of it separated the rest will be easy.  Polyester to polyester bonds have very little strength in tension.  It is almost scary.

Failing that I would use a dremel tool with a large cutting disk for the solid glass on the top edge and then grind out the remainder, and probably a cutting disk on a grinder and cut lots of slots then chisel out in between the slots for the rest.

You could try a combination - cut and chisel out a bit near the middle of the boat, then when you chisel out the wood the inner edge of the tabbing should be exposed.  That will make it easy to get your chisel under it.

Good luck!

 

[Rain Man]

BTW, my aft head conversion is more or less complete.  I will post a picture shortly.

 

[12 metre]

BTW, my aft head conversion is more or less complete.  I will post a picture shortly.

I would enjoy seeing that.  Might give me a few ideas as I`m planning on doing something similar as you know.

 

[tenders]

Agree that "bi-metal" blades make all the difference with oscillating saw tooling. Don't buy anything else except diamond-tipped if you're doing masonry, definitely not "high carbon steel."

In this job you can have any two of the following: fast, cheap, or clean. Your oscillating saw is cheap and clean, but it's slow.

My go-to tool for this purpose is a grinder with a diamond saw attachment. That's fast and cheap, but it throws a lot of dust. It works amazingly on fiberglass decks, bulkheads, G10, most everything, and lasts forever. Maybe for this application you'd want to hack out a little fence/guard so the blade can't get places you don't want it.

 

[12 metre]

Agree that "bi-metal" blades make all the difference with oscillating saw tooling. Don't buy anything else except diamond-tipped if you're doing masonry, definitely not "high carbon steel."

In this job you can have any two of the following: fast, cheap, or clean. Your oscillating saw is cheap and clean, but it's slow.

My go-to tool for this purpose is a grinder with a diamond saw attachment. That's fast and cheap, but it throws a lot of dust. It works amazingly on fiberglass decks, bulkheads, G10, most everything, and lasts forever. Maybe for this application you'd want to hack out a little fence/guard so the blade can't get places you don't want it.

I often used a grinder with cutoff wheel for fiberglass - goes through fit like a hot knife through butter.  But a bit too efficient for my liking - especially when cutting near the inside skin.  One slip could do a lot of damage.  But my main concern about using a grinder for cutting out as bulkhead is that I'm also cutting through plywood and I was under the impression there is no proper wood cutting wheel for a grinder.  A guy I know said he's done it, but with a lot of smoke.

Also use an Ultra-saw quite a bit for cutting straight lines in fiberglass and plywood.   Basically it is a grinder with a depth guide.  The drawback in this application is that it is only good for straight lines and impossible to get anywhere near a flush cut in this case.

 

[Diarmuid]

Lancelot!

(Mostly kidding.  These things will cut damn near anything really fast ... including skin, tendons, and bone. Awesome tools right up until they kick back & saw your arm off at the shoulder. Some people like them.)

 

[Steve Clark]

A  20 oz hammer does a really good job.

Seriously, wail away, stuff gets loose and can be peeled off.

SHC

 

[12 metre]

Lancelot!

(Mostly kidding.  These things will cut damn near anything really fast ... including skin, tendons, and bone. Awesome tools right up until they kick back & saw your arm off at the shoulder. Some people like them.)

I have seen that before but thought is was some type of martial arts or battle weapon.

 

[12 metre]

A  20 oz hammer does a really good job.

Seriously, wail away, stuff gets loose and can be peeled off.

SHC

A small amount of C4 would probably loosen things up pretty well too - but I am not going there either