stress cracks/splashwell modificaton

[Ezrider_92356]

well here is where im at now, i have a lot of stress cracks in the outer skin of my transom. i didn't really notice them till i really got to looking, i also have several holes that will not be re used, it looks like 2 different outboards have been mounted with different bolt paturns. different accessory's that have been mounted and removed sense 1958 to now some of witch were covered with an white silicone like substance. when i laminated my new transom in the peanut butter squeezed out all of the holes. i have now started sanding the outer skin with 40 grit sand paper and everything is smooth but it is down to the glass in some spots down to the original gel coat in others and still some paint in others and the peanut butter is sanded even to everything else. i am thinking of adding a layer of roving to the outside of the outer skin and then fairing it in, is this a good idea? and does everything need to be down to the glass or does my 40grit sand paper leave enough of a rough surface for good adhesion. another thing is i want to re locate my bilge drain lower, orrigionaly the TOP part of the stringer was notched and the drain just below the floor leaving about 2 inches from the bottom of the drain hole and the bottom of the inside of the hull. i want to put the drain plug as close to the bottom as possible, any concerns with doing this?

now onto the second part of my questions, my splash well, well i screwed something up, i test fit my splash well and the curve of my transom is off about a half inch. maby a little less. i must have eather made my clamping braces wrong or i should have exaggerated the curve to account for it coming back when releasing the clamps i laminated it one layer at a time. so now my spash well wont fit quite right. my thought is, to cut off the part of the splash well that meets the transom mount the spash well in place and re-make the back part to the splash well. maby using some kind of release agent between the two or a sheet of plastic or something to avoid actually bonding the two, what are your thoughts on this. or just throw the spashwell in the garbage and take advantage of the extra room..lol, (last resort)

 

[Driven1]

Re: stress cracks/splashwell modificaton

EZ, I'll return the favor on my thread and comment on yours.

On the stress cracks...

I was lucky and noticed mine after wiping down the inner skin with lacquer thinner so I put a couple layers of matt over it to seal it. In your case, because the transom is already in, I'd do this...

If you think of the mechanics of the transom you realize that the shell doesn't have much to do with the strength at the back of the boat. All of the strenghth is required in the corners where the transom meets the hull. The motor pushes on the transom and the force is transferred from the transom to the hull. So, other than the corners the rest of the skin doesn't do much. If you put on a layer of roving, you will end up with that distinctive roving look at the back of the boat. When the hull was manufactured, it was done on a smooth mold that allowed the resin to form a smooth surface when it was cured. There is a way to get that same smooth look though.

My suggestion would be to first glass in the extra holes and after leveling them, sand down to the rest of the skin glass and then put your roving on, rolling it good as you go. After it cures, feather any rough edges. Next cut a sheet of plastic in the shape of the transom that's a little larger by a couple of inches and have it ready for placement. Brush on another coat of mixed resin and then smooth the plastic over the resin being careful about air gaps between the resin and plastic. This will help hold the resin and keep it from sagging and also leave a nice smooth surface once the resin is cured and the plastic is peeled off. Prime and paint or gelcoat.

The drain...

I see no problem with moving the bilge drain. Just make sure that it's sealed in well with resin. I'd do that before doing the rest of the transom work.

The splash pan...

I'd kinda need a pic to see exactly what your talking about with the splash pan to give a suggestion for that.

Good luck.

 

[Ezrider_92356]

Re: stress cracks/splashwell modificaton

thanks i dident think of the plasic bag idea to make a smooth finish on the outter skin, the holes are all already conveniently filled in with peanut butter and iv sanded down the transom so all is smooth now even the holes filled with peanut butter. so i don't believe that i should need to glass the holes seperatly, although somone please correct me if im wrong, at this point i after doing more sanding on it today i could probably paint it and you would never know there was even stress cracks there, but for safety's sake i should probably add a layer of cloth or roving. probably roving because ill have it on hand. as far as the splash well goes i should get off my lazy *** and take the camera out there in the morning but for now ill try to describe whats going on a little better, the transom was designed to have an outward cure in it. if you put a straight edge across it the middle was about 2 inches out from the straight edge, well after building my transom i only ended up with about 1.5 inches. the splash well was a separate piece from the transom and the side that meeds the transom was molded to the same shape. as the transom and also includes the lip that goes over the top of the transom. and now that inner side of the splash well is about an half inch off from the shape of the transom. structurally i don't believe this is a problem. i threw an old 35hp jhonson on the back tilted it up and jumped on the lower unit with no flex in the transom and its not even tabbed in yet. so im looking for a way to modify the orrigional splash well to conform to the new shape of the transom.

 

[Ezrider_92356]

Re: stress cracks/splashwell modificaton

well i found an easy solution to my splashwell problem, while i was cutting my new stringers today i realized the splashwell is just fiberglass all i have to do is cut some relief cuts in the part that makes the transom cap and it should conform to the shape of the transom, so i tried it and sure enough worked like a charm, ill end up clamping in place with a plastic bag between the transom and the splash well fill the relief cuts with some matt wait for it to cure, after its cured i should be able to remove it add a layer of cloth or roving to the bottom side of the relief cuts sand the mat smooth with the orrigional glass and maby a little fairing compound and paint. its not a structural componte so it doesn't need to be super strong

 

[Driven1]

Re: stress cracks/splashwell modificaton

Cool beans! Doncha just love it when an idea just pops in your head. Glad you found a solution.

 

[ondarvr]

Re: stress cracks/splashwell modificaton

Since you're using polyester resin you need to use mat as the first layer of any laminting you do, so just cloth, or just roving, is not an option. If the crazing or cracks go all the way into the glass then it's best to glass over them, one layer of mat should do it, a layer of cloth over the mat can leave an easier to fair surface. 40 grit will work fine.

Using plastic sheeting sort of works on small surfaces, but on larger areas, it tends to leave a uneven surface that can require more fairing than using nothing.

The transom skins (layers of glass) add a great deal of strength and need to be strong. While cores (foam, wood, Seacast, solid glass) add strength in different amounts, it's the skins on either side, plus the thickness of the core that create the strength and stiffness.

The force applied to the transom is not in one direction (pushing forward), the top of the transom is pulled backwards and the bottom of the transom is pushed forward. If you hit something at speed with the lower unit these forces are reversed rapidly.

 

[Ezrider_92356]

Re: stress cracks/splashwell modificaton

thank you ondarvr for sharing your vast acknowledge. but to help me understand more why is it with poly you need to always use mat first where as with epoxy you don't have to? is it because epoxy gives a better bond? if my understanding is correct you use mat first because it fills in small voids better that cloth or roving, but if you are starting with a smooth (roughed up surface) how does the mat create a better bond. i don't imagine that the mat itself will go into the scratch marks left by the sand paper. i hope you don't take that as me questioning you because i'm not i know your an expert in this field i just want to expand my knowledge. I have blocked the whole transom and 4 inches of the sides around the transom with 40 grit where i plan on laying a layer of glass, its smooth and leval (well as smooth as 40 grit gets, but its all leval, iv done quite a bit of auto body work but not much of anything with glass other than fixing a few damaged fiberglass fenders where i filled the area with mat used cloth on the inside sanded and bondo'ed. witch brings me to another question is bondo acceptable to use for fairing on a boat if it is painted over or will the watter cause it to fail, i know body filler is porous but would be sealed by the paint. and im not talking about an 1/8 inch layer everywhere but just a very very thin layer in small spots to take out minor imperfections.

 

[ondarvr]

Re: stress cracks/splashwell modificaton

When cloth or roving is used as the first layer you end up with a layer of resin between the cloth and substrate whatever it may be. This resin layer is very brittle, polyester resin has little strength without glass, so when stressed this resin rich area fails. When mat is used there is at least some glass filling all (most) of the area between the cloth and substrate, so it's much stronger. In reality the resin bond is the same either way, because when the resin rich layer fails there's still resin stuck to the substrate.

Epoxy has much more strength on it's own, so no mat is needed.

Bondo isn't great stuff and it's a no no anywhere near water, it sucks it up like a sponge then falls apart. Areas that see no water may be OK for Bondo, but it's not very strong and may still crack and fall off.

 

[Ezrider_92356]

Re: stress cracks/splashwell modificaton

thank you again for another very informative post

 

[Ezrider_92356]

Re: stress cracks/splashwell modificaton

i spent about 6 hours today grinding prepping surfaces i have about a 1 inch thick layer of white powder about the consistence of flour inside of my boat and well just about everywhere in my shop, would this be suitable strain out any larger partials and then to mix with resin to make a fairing compound?

 

[ondarvr]

Re: stress cracks/splashwell modificaton

It will work fine, just don't plan on keeping any of the mixed putty around for long. The dust can react with the resin and it will start to gel, it can happen in a week or so if the conditions are right.

 

[Ezrider_92356]

Re: stress cracks/splashwell modificaton

cool, that will help out i'm already over budget so anywhere i can pinch a penny and still get good results will help.