1971 170 Aquasport Rebuild

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
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Rickk
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1971 170 Aquasport Rebuild

Post by Rickk » Wed Dec 26, 2012 7:43 pm

Hi All,
I am a long time lurker here and watched with great interest as the flatback was rebuilt.
I am starting a rebuild of a '71 170 Aquasport which I've owned since '88 and actually did a little restoration on it in '98 (new floor and stringer repair) and facelift in '00.
This is what the boat looked like in '00 when I was done and for the most part looks the same today, from the outside at least.
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I started to get some floor deterioration where the floor met the casting deck and I dove in and cut the floor out
Here is what it looks like now:
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and eventually this - the point of no return.I will lam 2 layers of new glass on the inside of the hull before I start stringer rebuilds.
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I have added some layers to the inside of the transom and just 2 days ago put in the new transom core (2x3/4" marine ply with 3/4oz, 1708, 3/4oz between it).
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You can see the clamping going on and my buddy Ed, mixing some more resin for new stringers.
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I found an old "new" 27gal Inca belly tank for the boat - this boat always had a tank inside the console above the floor so adding this will free up a ton of room in the back of the boat.
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This is where my questions begin.
I decided to make some forms for new stringers to match the shape of the originals and I made two forms - one with angled sides on both sides and one with a 90 on one side and an angled on the other. Got the idea here on this site (Maddog). :D
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The pic above with Ed shows the double angled form getting ready to lam it up. I lam'd 1 continuous 1708 and then added the cutoff of 1708 in the bottom. Then I added a 12" piece of 1708 on each side overlapping the corners. Topped the bottom off with 2 layers of 6 or 8oz mat.
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Here is the 90 degree one - look at the other end and you can see the 90.
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So anyway, I'm getting the pieces of the puzzle together and now need to figure out the exact stringer layout. I had 3 stringers as seen in one of the pics above. but I don't think I can use 3 anymore due to the tank.
The following drawing is what the thought is
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I know that I need continuous longetudinal stringers for strength and I think I can fit 2 in.
The stringers I made are 5.5" wide at the top and about 9" wide at the bottom and are roughly 11-12 inches deep. I would like to raise the floor an inch or two to facilitate self bailing - as she sits right now (see top pic) the scuppers are under water at rest. Plus I'll need that height to accomodate the new tank.
The drawing shows that the chine width at the transom is 63" and it starts narrowing and at the front of the tank is 55".
If I move the stringers in from the outside 14" (outside stringer top measurement) I think I can can get about 135" of stringer before they disappear into the hull. This unfortunately runs through the tank so here is my question.
At the top of the drawing you can see the profile of the stringers and the profile of the tank. I need to notch the tank a couple inches into each stringer to allow this to work - will that still give me good strength? I will glass the cutouts back in, inversed as a ledge.
I will use the 90 degree stringers as bulkheads for and aft of the tank.
I think I supplied enough pics to give you a good idea of how she sits in the water, the old stringers and drawings to help you visualize the plan.
The console back edge was 64" from the transom so that is where I started the back of the tank - might move it forward 2 more inches to allow the pie cover for the fuel feed and guage to be inside the console flooring.

Any questions? I'm hoping you guys can help me out here.



AtTheBrink
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Re: 1971 170 Aquasport Rebuild

Post by AtTheBrink » Wed Dec 26, 2012 10:01 pm

Looks like you got yourself a pretty good project! Your tear out looks great. Surprised to see 3 box stringers in a 17 foot boat. 8O . Is that polyester resin you are using?
Mike

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Matthew 4:19

Rickk
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Re: 1971 170 Aquasport Rebuild

Post by Rickk » Thu Dec 27, 2012 7:06 am

Hi Mike.
Yes - poly resin.
This is the first year of the 170 model - I think this is actually a late '70 model registered as a '71. The model was a shrunken 22 ft design and has the 12degree deadrise vs the flatback that was made at the same time.
The boat has been a solid boat for the years I've owned her - just time to bring her forward in conveniences, like under floor tank.
This thing has a MAJOR liner in her too
Image

You can follow the rebuild in more detail here.
http://www.classicaquasport.com/phpbb3/ ... =2&t=10101

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Re: 1971 170 Aquasport Rebuild

Post by Rickk » Mon Dec 31, 2012 6:53 pm

Happy new Year :D

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Re: 1971 170 Aquasport Rebuild

Post by DAYTRIP » Tue Jan 01, 2013 8:49 pm

Hey Rick, I am doing my second 17 mako right now so know what you are going through. Couple thoughts from me. I think cutting the stringer down 2 inches would be ok as typically 4 -6 inch tall stringers are saficient. You need several more layers of 1708 to get the strength you need though. If I read correctly you only have 1 layer? I would have at least 5 per side. I always like to do one of the layers with 1808 to give multi direction capacity. If you are removing the center stringer I would make sure your bulkheads cut the hull skin span to the same as the distance that was there with the center stringer. The other thing that I actually copied from the OB 15 I built was put flat stringers on each side of the keel. I used 3/4" by 4 " wide. There are ways to calculate all of the minimum requirements but i doubt you will get those answers here.

Use epoxy to tie the stringers to the hull for sure.

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Re: 1971 170 Aquasport Rebuild

Post by Rickk » Wed Jan 02, 2013 5:44 am

DAYTRIP wrote:Hey Rick, I am doing my second 17 mako right now so know what you are going through. Couple thoughts from me. I think cutting the stringer down 2 inches would be ok as typically 4 -6 inch tall stringers are saficient. You need several more layers of 1708 to get the strength you need though. If I read correctly you only have 1 layer? I would have at least 5 per side. I always like to do one of the layers with 1808 to give multi direction capacity.
Thanks for the reply Daytrip.
Right now I have 2 layers of 1708 to start and planned a couple more. I need to scribe them to the hull and once that it done I will put at least 2 more on. Was also thinking 1808 but wasn't sure if it is too late or not. I did read an article that said that the 45 +/- of the 1708 supported the stresses as well as 1808. I understand the theory of the fiberlay differences.
DAYTRIP wrote:If you are removing the center stringer I would make sure your bulkheads cut the hull skin span to the same as the distance that was there with the center stringer.
You lost me here. :doh:
DAYTRIP wrote:The other thing that I actually copied from the OB 15 I built was put flat stringers on each side of the keel. I used 3/4" by 4 " wide. There are ways to calculate all of the minimum requirements but i doubt you will get those answers here.

As in laying flat on the hull?
DAYTRIP wrote:Use epoxy to tie the stringers to the hull for sure.
I planned on doing everything in poly.

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Re: 1971 170 Aquasport Rebuild

Post by tech_support » Wed Jan 02, 2013 10:06 am

Rickk wrote: I planned on doing everything in poly.
Even tabbing it all together?

We try very hard to keep the advise here consistent. We do not recommend poly for rebuilds, or at least for any secondary bonding. making stringers or other parts from poly, then bonding them in with epoxy is a fine idea, but I would not invest all the time and money in a re0-built to have it all being held together with polyester secondary bonding.

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Re: 1971 170 Aquasport Rebuild

Post by slvrlng » Wed Jan 02, 2013 3:04 pm

shine wrote:
Rickk wrote: I planned on doing everything in poly.
Even tabbing it all together?

We try very hard to keep the advise here consistent. We do not recommend poly for rebuilds, or at least for any secondary bonding. making stringers or other parts from poly, then bonding them in with epoxy is a fine idea, but I would not invest all the time and money in a re0-built to have it all being held together with polyester secondary bonding.
Ok Joel, how can he tab the stringers down with epoxy then lay more 1708 across the whole stringers since the poly usually won't stick to the epoxy? Or should he abandon the poly for this purpose entirely. He has 10 gallons of poly left and no epoxy at this time.

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Re: 1971 170 Aquasport Rebuild

Post by tech_support » Wed Jan 02, 2013 3:28 pm

how can he tab the stringers down with epoxy then lay more 1708 across the whole stringers since the poly usually won't stick to the epoxy?


you would need to make the stringers from one poly lamination = one piece, then tab them in with epoxy. the way its described now, there will be a secondary bond on the tabbing of the stringer to the hull, then a separate bond with the wide cloth going over it all. I would not recommend that.
He has 10 gallons of poly left and no epoxy at this time.
Even if you had 100, it would not have an effect on my advise. Epoxy for all secondary bonding.

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Re: 1971 170 Aquasport Rebuild

Post by Rickk » Wed Jan 02, 2013 7:36 pm

Thanks for the reply Joel. Happy New Year.
(Thanks Lew for trying to explain this)
shine wrote:you would need to make the stringers from one poly lamination = one piece, then tab them in with epoxy. the way its described now, there will be a secondary bond on the tabbing of the stringer to the hull, then a separate bond with the wide cloth going over it all. I would not recommend that.
It sounds like I have made a mistake here in that I have made 2x6ft stringers and then joined them and have done that for both of the stringers. I also wanted to make one more and cut it in half and then add each half to one of the stringers. All of this would be a kind of shell or form for the full length peices I would lam onto them later.

If I did lam the entire lengths of these stringers with a couple layers of cloth (in poly) to get a solid stringer would it then be able to be epoxy tabbed into the hull? Would you then continue to epoxy lam (to include the tabbing) some big cloth over the stringers to bond everything to the hull?
Is there any way to salvage and use what I've made so far?
He has 10 gallons of poly left and no epoxy at this time.
shine wrote:Even if you had 100, it would not have an effect on my advise. Epoxy for all secondary bonding.
I guess I could save this for something else above deck (I will be gelcoating this boat). I have not done the entire inside hull lam yet.

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