Transom layup/composition questions

[gw204]

On my 170, the thickness of the outer transom skin is a hair over 1/4" at the bottom and just over 1/8" at the top.  This took me by surprise as I was expecting uniform thickness throughout.  But, now that I took another look at it, this difference in thickeness may just be at the area where I placed the cut and might actually just alleviate some grinding for me.  The glass is nice and thick where the lifting eyes were mounted to the transom, which is closer to the sides.

Anyway, when I start putting the transom back together I plan to make sure the outer sking thickness is uniform at 5/16" to 3/8".  When done, she's going to get either a 90 or a 115 at up to 375 lbs.  So, if I make the inner skin the same thickness as the outer skin and add 1-1/2" of core (marine ply or Coosa Bluewater 26), will it be strong enough, or overkill for that motor weight?  If overkill, could I cut back to 1/4" on the inner and outer skins to save a bit of weight?

I know it's probably going to end up with a heavier transom than original though.  When I opened it up, I found the inner skin was only a single layer of heavy cloth...

Anyway, when I cut the outer skin off, I left a 6" lip on the sides and bottom.  I was planning to bevel this lip the full 6" to allow the new glass to bond to the existing.  The new skin would consist of a layer 3/4 oz mat, then mulitple layers of 1708 or 1808 with the final layer being layer being 3/4 oz. mat.  Then core, then basically the same thing for the inner skin.  Sound good?

Is that 6" lip enough, or should I do it another way?



Lastly, so I can order the right amount of materil to do the job...

1.  How many layers of 1708 or 1808 will I need to get my desired skin thickness?
2.  In general, is there a ratio of how much resin (I'll be using epoxy, not poly or vinyl) a certain size piece of biax. requires to adequately wet out?
3.  How far up the hull sides and bottom should I wrap the new inner skin?  I was thinking 2 addl. inches for each progressive layer.
4.  Any recommendation on where to get my glass and resin?  Raka, US Composites, etc?

Anything else I need to consider?

Oh, one more thing.  What discs are you guys using on your grinders?  Those heavy duty "sanding" type discs similar to you would see on a random orbit, but in 36 or 50 grit, or is there something else?

Thanks.

[LilRichard]

On my 170, the thickness of the outer transom skin is a hair over 1/4" at the bottom and just over 1/8" at the top.  This took me by surprise as I was expecting uniform thickness throughout.  But, now that I took another look at it, this difference in thickeness may just be at the area where I placed the cut and might actually just alleviate some grinding for me.  The glass is nice and thick where the lifting eyes were mounted to the transom, which is closer to the sides.

Anyway, when I start putting the transom back together I plan to make sure the outer sking thickness is uniform at 5/16" to 3/8".  When done, she's going to get either a 90 or a 115 at up to 375 lbs.  So, if I make the inner skin the same thickness as the outer skin and add 1-1/2" of core (marine ply or Coosa Bluewater 26), will it be strong enough, or overkill for that motor weight?  If overkill, could I cut back to 1/4" on the inner and outer skins to save a bit of weight?

I know it's probably going to end up with a heavier transom than original though.  When I opened it up, I found the inner skin was only a single layer of heavy cloth...

Anyway, when I cut the outer skin off, I left a 6" lip on the sides and bottom.  I was planning to bevel this lip the full 6" to allow the new glass to bond to the existing.  The new skin would consist of a layer 3/4 oz mat, then mulitple layers of 1708 or 1808 with the final layer being layer being 3/4 oz. mat.  Then core, then basically the same thing for the inner skin.  Sound good?

Is that 6" lip enough, or should I do it another way?  



Lastly, so I can order the right amount of materil to do the job...

1.  How many layers of 1708 or 1808 will I need to get my desired skin thickness?
2.  In general, is there a ratio of how much resin (I'll be using epoxy, not poly or vinyl) a certain size piece of biax. requires to adequately wet out?
3.  How far up the hull sides and bottom should I wrap the new inner skin?  I was thinking 2 addl. inches for each progressive layer.
4.  Any recommendation on where to get my glass and resin?  Raka, US Composites, etc?

Anything else I need to consider?

Oh, one more thing.  What discs are you guys using on your grinders?  Those heavy duty "sanding" type discs similar to you would see on a random orbit, but in 36 or 50 grit, or is there something else?

Thanks.

I will answer a few questions...

1/4" should be fine for inner and outer skin- that's (someone chim in please) probably 4 layers of 1808 or so.  I used 4 layers for my inner skin, overlapping at about 1.5" to 2" each layer.

The 6" lip is plenty- you're shooting for at least a 12:1 scarf (versus laminate thickness), but more is always better.  6" gives you a 24:1.

I use a resin grinding disk, like this:



I get those disks, along with all my materials, at FGCI- http://www.fgci.com

[gw204]

Great!  Thanks man!

I've been following your project both here and a ClassicMako.  Nice work!  Where did you get the foam for your stringers?  That's something I'm considering as well.   :)

[LilRichard]

Great!  Thanks man!

I've been following your project both here and a ClassicMako.  Nice work!  Where did you get the foam for your stringers?  That's something I'm considering as well.   :)

Thanks GW.

I got the foam from a local fiberglass supply shop- http://www.fgci.com

It's 3 lb polyurethane foam... easy to work with- I would recommend it.

[gw204]

Cool, thanks.  I completely forgot about FGCI.  :-)

I'm sure those things are economical to ship though.  Maybe I'll have to buy the pour foam and build my own molds.  But we'll see.

[LilRichard]

I think you can prolly find the sheets somewhere else.  If you decide to pour foam, I wouid suggest following Wilson Ayala's method from the CM site.  He built the stringers on a form, tabbed them in, then filled with foam.

[JimCt]

Maybe I missed something here but what's wrong with the stringers you've got?

Leave them where they are, pull the foam out of them, retab to lock them down hard then pour in your new foam.

[Shine]

I would try to brace the hull before taking out any more of the sole

[gw204]

Thanks Shine.  After the transom is done, I'm going to pull it off the trailer and set it on a bunch of closely placed cinder blocks under the keel, with addl. supports placed under the chines.  Sound good?

Also, what do you think of my plan for the transom?

Thanks.

[gw204]

Maybe I missed something here but what's wrong with the stringers you've got?

Leave them where they are, pull the foam out of them, retab to lock them down hard then pour in your new foam.

It's not that there's anything wrong with them, aside from some tabbing that has broken loose near the transom (who knows what's going on with the parts I can't see yet though) and wet foam, I'de just like to reconfigure things a bit for added floor support and to stiffen the hull a bit more.

[LilRichard]

I would not take the stringers out if they are not bad... you'd be getting yourself into a lot of work for little benefit IMO.

If I could have kept my stringers, I certainly would have...

[Shine]

1.  How many layers of 1708 or 1808 will I need to get my desired skin thickness?
2.  In general, is there a ratio of how much resin (I'll be using epoxy, not poly or vinyl) a certain size piece of biax. requires to adequately wet out?
3.  How far up the hull sides and bottom should I wrap the new inner skin?  I was thinking 2 addl. inches for each progressive layer.
4.  Any recommendation on where to get my glass and resin?  Raka, US Composites, etc?

Anything else I need to consider?

Thanks.

1) you should shoot for close to 1/4" for the outside skin, use 1708 or 1810 for that (builds up thickness with the mat), then switch to Db1700 and LT1800 (same stuff but without mat) for the inside.  If you using epoxy the mat is not really needed.

2) In general your shooting for 50/50 by weight.  the more may you use the more resin it soaks up though.

3) first layer 4" then 2" progressing from there

4) I would humbly submit my store as a choice also

Sorry it took so long to respond - been at the boat show for the last week

Joel

[gw204]

Thanks.

Haven't made any addl. progress lately.  It's been too darn cold.   :(

[JimCt]

Same here.  Problem is, when good weather finally shows up projects around the house need doing too.

[gw204]

Tell me about it.  Right now, I'm knee deep in a bathroom floor project, a laminate floor project and repainting of my living room and downstairs hallway.   :(