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Happy New Year everyoneÔǪ..for a 2012 project I'm thinking about finally straightening out my engine hatch cover (2855) which has a ┬¥ inch bow downwards in the middle, it would sure help the sound attenuation! Has anyone done this? Any Ideas?
Dave, if you are saying that the hatch dips in the center, or is concave, I understand. I have the same issue, and will someday correct it.
As mine is now, it pools water, and I don't like that.
As for sound attenuation, guess I'm not following you on that one, unless the perimeter is not closing against the main deck gutter area.
But for whatever the issue is, I've spoken with a pro regarding the fix, and here's what he suggested.... paraphasing it.
Cut open the under-side of the hatch fiberglass and expose the core around it's perimeter, and remove all of the old core material.
Clean this up right down the under-side of the hatch (the underside of the exterior surface).
With the core removed, you should be able to now flex the surface.
Make new core material and pre-fit it.
Place the hatch upside down on a flat concrete surface supporting each corner equally off of the concrete.
(he did not say how much, but I'm thinking an inch or so)
Key: with a pre-determined length post that contacts your shop ceiling structure, adjust so that the post length creates the new "Convex" that you want.
One single post right in the center of the hatch........ and use shims for final adjustment.
Allow for thickness of core, matting and resin (roving can be applied afterwards).
Lay up the new core material with matting/resin and assemble.
Quickly install the post and check your convex....adjust with shims.
The post pressure will create and will maintain your new 'convex' surface on the top side once all has cured.
Sounds simple, however, I've not done this yet......, but it sure makes sense that it would work.
.
Rick E. (aka RicardoMarine) Gresham, Oregon
2850 Bounty Sedan Flybridge model
Twin 280 HP 5.7's w/ Closed Cooling
Volvo Penta DuoProp Drives
Kohler 4 CZ Gen Set
I wouldn't shoot for 'convex' as Rick describes, but you can easily remove the material with this trick. Purchase a sheet of cheap luan skin. Remove and flip the hatch onto a flat surface. Set your router depth to cut through the filler material but preserve the glass skin below. Measure out stripes about 4" wide and 1" apart across the deck. Cut those rows of material about 4" or so wide out with the router. You'll be left with the 1" stripes of remaining material. Then adjust your router bit to add the depth of the luan sheet (.125" usually) and then mark the luan to locate the stripes you have left and clamp it the hatch. Cut through the luan in the areas that you marked to get the stripes that are left. Remove the clamps and discard the luan and you should have routed out all the old material to a consistent depth.
If you encapsulate a quality sheet of 3/4" ply with polyester resin, it should come out dead flat. I wouldn't wanna shoot for 'convex' because it'll eventually oilcan on ya and you'll be right back where you started.
Hello Dave I re cored mine a few months ago this is how I did it if you want to go this way it worked out great .I used a zipcut disc on the grinder and cut around the top leaving a 3/4" lip and scraped,chiseled and grinded out the old plywood saving the original outer fiberglass skin,cut out new replacement piece.bevel top edge. sand and clean cover and skin,lay on fiberglass mat inside cover on a very level garage floor or equivalent wet out with lots of resin with a slow cure so it can sok in good ,insert new core place weight on top let set for 24hrs.I covered the top of the plywood with another layer of thin matting cut to extend to the outside edge of cover wetted out and replaced the original skin over the resin and matting then added weight.After all cured sanded the edges.I brushed on gelcoat then sanded.I was worried that it wouldnt be straight when I reinstalled it but it layied in perfect, lots of weight is important.
Thank you guys for your responses. Looks like you did a real nice job Prairie. Your replies gave me a lot of possibilities to ponder. One things for sure though, It's not going to be a straightforward job! (is anything on a boat?.....?)
Dave, I agree with using a router as Mike suggested. That's been mentioned here many times for when removing old transom core material.
Straight flute cutter, set to the correct depth, cut into smaller sections and chisel/scrape/grind it out of there.
A small pneumatic chisel works nicely.
I can tell you first hand that this approach works very well.
I would, however, question why we would not want a slight convex to the newly re-built hatch lid!
Given a choice between flat or slightly convex, I'll take a slightly convex surface!
You won't notice it by eye......, but any water on the hatch will realize it, and will run off into the gutter!
Mine is stout structurally, but it holds water in the center, and it bugs me.
Mike, perhaps you were you thinking that the 1" dimension was being suggested for the convex ...... Not so!
The 1" would be the dimension off of the concrete floor at each of the four corners.
Then perhaps a 3/4" spacer in the dead center, netting a convex of 1/4", or so, as the center post presses downward during the curing.
I'd think that 1/4", or even 3/8", would do nicely for the convex.
.
Rick E. (aka RicardoMarine) Gresham, Oregon
2850 Bounty Sedan Flybridge model
Twin 280 HP 5.7's w/ Closed Cooling
Volvo Penta DuoProp Drives
Kohler 4 CZ Gen Set
2850Bounty wrote:
Mike, perhaps you were you thinking that the 1" dimension was being suggested for the convex ...... Not so!
The 1" would be the dimension off of the concrete floor at each of the four corners.
Then perhaps a 3/4" spacer in the dead center, netting a convex of 1/4", or so, as the center post presses downward during the curing.
I'd think that 1/4", or even 3/8", would do nicely for the convex.
Nope. Not thinking that at all. I just think it would be better dead flat as it was laid up originally. If I had that problem here, I could remove the old material in minutes on my CNC router. Just clamp it and draw up a pocket deep enough and turn on the dust collector.
Not sure if you got the term "oil canning" I warned of, but that would be my concern with trying to force in a curve in something that was cast flat.
Nope. Not thinking that at all. I just think it would be better dead flat as it was laid up originally.
Not sure if you got the term "oil canning" I warned of,
but that would be my concern with trying to force in a curve in something that was cast flat.
1 wrote:
Mike, I don't know if these were intended to be laid up flat or with a slight convex to them, as I've never actually checked a brand new hatch surface.
The topic is rebuilding an existing one that is now "concave"........ and I'd certainly NOT want one to be flat or concave, and/or to collect and hold water.
Perhaps this is not an issue for some of us........, and if that's the case, take my suggestion and toss it out the window!
Simple as that!
But appartently he wants to rid this of the concave surface.
Of course... most of us are familiar with that term.
Any "oil canning" is to be prevented via the "Box Beam" design that can't help but be incorporated the moment that a "core" is properly laid up..... just as with a transom core.
Think "Box Beam" or "Torsion Box", Mike!
That's what the glass/core/glass becomes once laid up.
Cast Flat..... as in a "casting"?
Mike, we're talking about 1/4" here, not 1" !
That's only .250", or roughly the thickness of a carpenter's pencil.
That is not unrealistic at all!
If you think that 1/4" has the potential to stress and damage this hatch surface......, then you'd best start over and build a new one.
Consider this:
While the hatch has been stripped out, and is laying falt on a concrete surface ready to rebuild...., I doubt that any of us can 100% predict the outcome of this lay-up once the new core has been laid and has cured.
Sure.... there may be some predictability here... but how much?
I'd much rather space it and shoot for a slightly "convex" surface, and end up with a "flat" surface..... than to NOT space it, shoot for "flat" surface, and then end up with a slightly "concave" surface!
I would not want mine to pool water if I could prevent it.
.
Rick E. (aka RicardoMarine) Gresham, Oregon
2850 Bounty Sedan Flybridge model
Twin 280 HP 5.7's w/ Closed Cooling
Volvo Penta DuoProp Drives
Kohler 4 CZ Gen Set
I think that all your comments are pertinent, but I have to go back to my reason for wanting to do this. I'm not concerned about water pooling in the middle of the hatch because my boat is back heavy (as are most 2855) and theres enough slope front to back.
What bugs me is that the two corners, opposite the hinge side, protrude up through my new Corinthian Carpet (Awesome company by the way) Furthermore, when the carpet is removed for fishing trips the engine noise level is signficantly reduced when someone stands on the hatch corners, closing it against the hatch seal.
This is not a structural problem but I guess is probably due to shrinkage when the glass lay up dried out. I'm tempted to consider routering a groove across the middle of the hatch, filling with Glass, then prior to drying, bolting a piece of2 x 2 x 1/4" Aluminum angle at R/A to this along the Hatch length. Any thoughts????
What makes the hatch surface stout enough to support people, is the Box Beam affect that I've mentioned.
This means the top skin (all of that fiberglass and it's thickness)..... the center core (the material that separates and spaces the top and bottom "cords")... and the underneath skin ( layers of matting and/or heavy cloth) are adhered together by the resin wet fiberglass material.
The skin/spacer/skin creates this box beam (or torsion box) since the two cords (skins) resist stretching or compressing.
A box beam is intended to be more stiff, whereas a torsion box is to be more flexible..... but you can see the idea.
I suppose that a laminated Archery Bow is along the lines of a torsion box..... and a painter's scaffolding "pick" is along the lines of a box beam.
If you sliced the bottom skin into sections, the hatch will flex even more so.
If you then straightened it out like what you want, you may be able to lay up matting/cloth on the underside, and stiffen it back up when it has cured.
As long as you're this far into it, why not space it off of the floor, and give yourself either a flat or convex surface?
Rick E. (aka RicardoMarine) Gresham, Oregon
2850 Bounty Sedan Flybridge model
Twin 280 HP 5.7's w/ Closed Cooling
Volvo Penta DuoProp Drives
Kohler 4 CZ Gen Set
2850Bounty wrote:
What makes the hatch surface stout enough to support people, is the Box Beam affect that I've mentioned.
Laminating a sheet of plywood onto thin layers of fiberglass doesn't make a "box beam". You've got a simple lamination. Heck, the way you explain it that way, the plywood all by itself is a box beam.
2850Bounty wrote:
As long as you're this far into it, why not space it off of the floor, and give yourself either a flat or convex surface?
Or... you could replace the rotted or warped ply and have a flat hatch again. Just like new.
Try the convex trick and you'll oil can sooner or later and have a puddle. You want that hatch to be flat so that any flex in either direction will put the panel in compression and tension. I'd be shooting for drum flat myself.
bristleboy wrote:
Thank you guys for your responses. Looks like you did a real nice job Prairie. Your replies gave me a lot of possibilities to ponder. One things for sure though, It's not going to be a straightforward job! (is anything on a boat?.....?)
Cheers,
Dave
Oh how very true.I have done a few jobs on my boat that didnt take the first time and were total redos but of course I dont tell my friends at home this LOL.Using a router absolutely sounds like the best way to go.Lots of smart Bayliner owners on this site I am always learning something new.My cover is a half inch high in the middle now guys after a flat set three mths ago? I think the tension in the glass theory after forcing it flat slowly concaves the cover up somewhat close to original position over time with assistance from the sun making it malleable is starting to hold weight.
SomeSailor wrote:
Laminating a sheet of plywood onto thin layers of fiberglass doesn't make a "box beam". You've got a simple lamination. Heck, the way you explain it that way, the plywood all by itself is a box beam.
Or... you could replace the rotted or warped ply and have a flat hatch again. Just like new.
Try the convex trick and you'll oil can sooner or later and have a puddle. You want that hatch to be flat so that any flex in either direction will put the panel in compression and tension. I'd be shooting for drum flat myself.
+1 keep it flat if you make it convex it will end up an oil can and then you will be really *issed.
All Dave asked for were a few suggestions re; how and what to do with his hatch that is not sealing well, and with the sound attenuation issue.
Then upon my reading that Dave's hatch is concave, I made a suggestion as to not only what I would do, but what a "Pro" would do. (Pro being the person whom I spoke with, and who performs this work professionally)
So when it's suggested that a convex not be the goal or not be incorporated....., it just seems counter intuitive to me.
Dave, if you're still on board, you've heard from several sides of the table now.
I hope whatever you do works out well for you.
.
Rick E. (aka RicardoMarine) Gresham, Oregon
2850 Bounty Sedan Flybridge model
Twin 280 HP 5.7's w/ Closed Cooling
Volvo Penta DuoProp Drives
Kohler 4 CZ Gen Set
I rebuilt a rotten swim platform on a dock-neighbour's boat, and we put in a bit of convex shape.
Many holes drilled in the top skin over the years had allowed moisture in, and rotted the core of end grain balsa. I fixed those holes before beginning on the underside work.
As described above, we removed the old coring without damaging the top surface, using a circular saw, router, chisels, grinding and sanding. All work was done from the underside (flipped over, of course). It was messy and unpleasant but not technically challenging.
After removing the core, we laid the platform upside down onto a nice flat cement floor. We used a level and a string to see how flat and level the floor was.
When we had the new layup cut to size and dry-fitted, ready to go in, we supprted the perimeter of the swim platform on wood blocks that we had cut to be 2" high. We used the 2" blocks only around the outside of the platform. There were a bunch - 10 or more around the periphery; I forget exactly how many. It just looked "right". We cut 2 blocks shorter - I think by about 3/16" - and put those under the platform, on the centreline, near the middle. Once we had the layup done, we loaded on full paint cans as weights and this the middle of the platform down the 3/16" until it rested on the 2 lower blocks, effectively pre-stressing the system.
That platform came out great. It drains well and doesn't oilcan. The thickness is roughly 1 1/4" total so it really can't oilcan as long as there's good adhesion between the interstitial layers and the original 'glass top skin and new bottom skin of glassfibre cloth. That will be 7 years ago this Spring, and it still looks perfect.
...... Not so!
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