1980 cobia gulfstream

[ezmobee]

Re: 1980 cobia gulfstream

yeah, it's not fiberglass reinforced adhesive, it's adhesive for those fiberglass reinforced panels. Probably very similar to PL.

 

[logan944t]

Re: 1980 cobia gulfstream

Figure Id post an update.


Demo work continues--I usually get 3 or 4 hours a day work in.

One of the questions I asked before was about the hollow glass boxs on either side of the main stringers was for. GT guessed battery tray and I think thats the one Im gonna go with.




As you can see from the closeup, it contained compost and leaves and under all that --there were a few fishing hooks and a lure.


If you look close you can see a hole where the stringer wood used to be. Anytime there was water in this square space it would wet the stringer wood.


This is a shot of the main stringers from the transom hole with the glass partially removed. I had used a chisel to cut the stringer back from the transom to remove the rotted wood. When I first cut into the stringer down low with the air grinder --water came gushing out. I was confused because there was no water any where else.

 

[chriscraft254]

Re: 1980 cobia gulfstream

Subcribed

 

[logan944t]

Re: 1980 cobia gulfstream

The reason for the water IN the stringer was because the stringer was not a solid chunk of wood, but rather a stapled together layering of 3/4 " plywood that was resting on 2 strips of 1" wood that was resting ( NOT glassed) on the hull. Anytime the battery tray had water in it --it would also find its way in between the 2 pieces of wood enclosed under the main stringer glass.


Shot of a main stringer from the transom hole with glass removed.


I was able to remove the rest of the OSB from under the aft fuel tank area. The hull shifts a bit when I walk on it now.



This is looking straight down along the transom. There is still a layer of wood that I have to remove with my belt sander but the bottom of the transom has been feathered. If someone can tell me what kind of gray coating that is I would appreciate it. The glass would grind away fairly quickly but that coating would hang on and be real stubborn.



Transom/side joint still needs a bit of feathering and this space is the most difficult to work on. The combination of the breeze from the grinder, the air filled with glass and the sun on my goggles and Im mostly blind when working here. On the upside, there is no more itch on any exposed skin I have.


I have to say that the grinding disc that Im using is one of the best Ive used. Its 4" 1/2 40 grit "Diablo" with the numerous folded over flaps on it. I have no doubt that I could grind thru the hull in a matter of seconds.


Happy New Years to everyone!!

 

[logan944t]

Re: 1980 cobia gulfstream

You should try a rubber back up pad and 36 grit resin impregnated sanding discs. Now THAT's Hot butter grinding. Harbor Freight sells em for less than 10 bucks.

Ya know Mr wood, I normally would go right out and buy one of those --just to get the experience and a new tool of course. But Im in one of those situations where one more tool is gonna explode my tool box --so I would have to buy a whole new tool box. Since I like uniformity, I would have to get one on wheels to match the other 3 I have ( Tower of Tools!!)......then I would have to build an addition onto the shed to keep it out of the rain......so you see......Im going to the bank on Monday for a loan for a new garage....then stop at the lawyers to sign the divorce papers IM sure the wife will throw at me for ....buying just one more tool. Is there a support group? Or a med I can get?

 

[logan944t]

Re: 1980 cobia gulfstream

I moved the boat around on the cradles today --and got some blue sheet foam under the hull to cushion it some.

I noticed that the hull is a bit.....off. Not by much-- and looking by eye you cant really see it but when measured by the cradles( which, admittedly could be off a bit) one chine is 1/4" off the cradle when the other is on. I measured from the concrete pad underneath the boat and its off by almost that.


Is this normal?

 

[tosoutherncars]

Re: 1980 cobia gulfstream

Hi Logan,

I was surprised that some of the more experienced guys hadn't chimed in to suggest reinforcing the hull a bit more (supporting it at more points with braces). In some of your earlier pictures, you can see the outer hull surface sagging and bending; of course, the more you cut away, the less structural rigidity the hull has, and the more it is likely to shift. Guys usually seem most worried about this when they're cutting the cap off; but taking out the entire floor, parts of the gunwales, stringers and all of the structural strength of the transom surely creates similar issues.

Please keep updating; I've got a similar boat (Cobia 200SS center console) that I'm sure is in a similar state underneath. I've (hopefully) got a year or two before I make the decision to fix or sell (or scrap); great to be able to see a similar real-life resto.

Best,
Duncan, Ottawa

 

[logan944t]

Re: 1980 cobia gulfstream

Yea-- Im kinda worried about the hull moving around as well. When I first put it on the cradles it was touching all the uprights. Now there are spaces...which could just be the fact that Ive removed a lot of weight, or the hull is warping. If it is warping then it is only off by a 1/4 " or so. Most of the cap is still on --Ive removed the last 12" or so to get at the transom.

I noticed the other night that I can pick up the aft section of the boat with one hand now. I cant budge the bow section. Im hoping that this doesnt mean that the cap has wood thruout......

Not much to update--I havent had a chance to work on it till today and I was just grinding away the excess glass where the main stringers used to be.

Ive decided to make the section of hull where the motor used to be as flat as I can so I can glass in a layer of 1708. When I grind away the grey rubberized paint that the factory put in there are sections that are just one layer of woven roving.....which makes me nervous as hell. I have a 16' canoe that oilcan's with the same stuff. I cant imagine that a layer of gelcoat makes the roving that much stronger and this is where the boats sits when its up on plane. I know the hull shape is much different which adds strength....but its gonna get another layer at least.

Anyone know what the grey rubberized coating is?

Is there anyway to tell the difference between epoxy and poly when its on the boat?

 

[logan944t]

Re: 1980 cobia gulfstream

Got about 2 hours yesterday in between raindrops and started working on what I thought was a layer of wood left on the transom. Turns out that what I see is the imprint left by the wood in the resin. I was able to remove all the dry CSM that seems like it wasnt wetted out properly from the factory-- and that left a 6" strip across the top of the transom that is down to the roving.

The rest of the transom is a layer of csm and then roving --then the outer gelcoat skin. So I think what I have to do is glass in csm to bring both areas to the same level before I put on the 1708 then the new plywood transom.

 

[GT1000000]

Re: 1980 cobia gulfstream

Hi logan,
Just wanted to jump in and say...
1- great progress!!!
2- according to Woodonglass, you don't need the layer of 1708 between the hull and transom, just some PB...if in doubt PM him...or oops!...

 

[logan944t]

Re: 1980 cobia gulfstream

2- according to Woodonglass, you don't need the layer of 1708 between the hull and transom, just some PB...if in doubt PM him...or oops!...

I finished grinding on the transom yesterday. No pics I need a new sd card. The top 6" all across the top of the transom was not wetted out properly so I had to grind it down to good glass--which was the roving. So I need to lay a few layers of csm across the top to build that area up level with the rest of the transom.

I would prefer to not use the 1708 there--but if its not level enough to form a good bond with the plywood I have to build it up in some way to get that bond. Right now --at the top-- there would be a gap of about a 1/4".

Im also trying to visualize what the knees are gonna look like and incorporating aluminum knees into the brackett so that its all one unit--as well as a piece on either side that ties the sides of the boat into the inner transom design.

 

[Woodonglass]

Re: 1980 cobia gulfstream

Why R U wanting to put Aluminum Knee braces in a Glass Boat? How would you attach them? Glassing over aluminum is not a good idea. Mechanical fasteners into the transom is just asking for future problems. I'd stick with Plywood knees properly fabricated and glassed. They will outlast you. You do need to build the stern skin back to as flat of a surface as possible before you glue the transom in place. CSM and 1708 or Woven roving would be my choice to do this as well. When you're ready to install and the transom wood is coated with resin and CSM then all that's required is a liberal coating of PB and then clamp the transom in place and fillet the edges.

 

[logan944t]

Re: 1980 cobia gulfstream

Why R U wanting to put Aluminum Knee braces in a Glass Boat?

The bracket that I want to hang on the transom will be aluminum and I want the extra strength.

How would you attach them?

Im visualizing an aluminum U channel across the transom ( port to starboard) where the bolts from the bracket ( and the swim platform) will attach. The aluminum knees will be bolted to the channel on the knees top side. The bottom of the knees will have a lag bolt sunk into the stringer from the top (sealed with 5200?). The bottom leg of the knee will have sides that are snug to the sides of the stringer and have a bolt and nut that runs port/starboard thru the stringer. IM hoping that the vertical bolts on the bracket will line up with the knees as well. The aluminum will not be glassed in.


Im aware that this is way overkill. The original transom was only 2" around the drive and across the top in a 4" wide section--but it didnt have to carry the weight and torque of an outboard. The transom Im gonna put in will be 3 layers of 3/4" acx properly soaked in poly and fully encapsulated in glass.

Essentially, the motors weight will be supported by the aluminum knees as well as the transom. Im also considering glassing in a horizontal "knee" that will connect the top of the transom to the port and starboard sides under the cap.

Mechanical fasteners into the transom is just asking for future problems.

Thru flexing and fatigue or rot?



Am I barking up the wrong tree as far as trying to overengineer this?