Flatback Fireboat Rebuild

[CLM65]

Thanks for the input Scott, Bob, and Cally.  Bob makes good points and I don't disagree with him.  But I will say, in my opinion, that eliminating the flotation foam (outside the stringers) does change the way the integrated structure behaves in a non-conservative way.  Does it affect it enough to make a difference?  Probably not.  But...I believe the stringer sides are the weak link, at least on my boat (I was being generous when I estimated up to an 1/8" thick).  Adding bulkheads beneath the deck joints was something I was considering anyway, so this just provides additional justification.  I don't believe adding Nida Core bulkheads with 1708 on each side will add appreciable weight.  And I don't think the cost will be too bad, relatively speaking.  And the extra work?  Heck, it just helps push off sanding the paint off the hull and cap, which is something I'm not looking forward to!

[Aswaff400]

if you look back in my pics you can see a 2-by-whatever i was using as a bench or to set the fan on set across the empty stringers, i would even stand on it to take pics. still felt solid... i added 1 to 2 layers of 1708 on the outside, and a layer on the inside bonding directly to the hull, she is a whole lot more solid now even without foam.i will be pouring foam some time this week, or early next week

[CLM65]

Yeah Aaron, the stringers are certainly stronger than I give them credit for.  But while I have the opportunity, I'm going to at least add some bulkheads for additional strength.

[gman 82 aquasport]

Great thing about this site, you get info from mutiple people and mutiple ways of doing things, none wrong, but in the end it comes down to you and your comfort of your rebuild...if more thickness on the stringers makes you more secure for the hull strenght then add more glass and resin, just don't go overboard.. if you look at most of the rebuilds on here you will find that many(myself included) added layers to the hull floor and or the stringers(I did both) right, wrong, don't know for sure but I felt better about it after doing it..That said if you will have more confidence in the structure with thicker stringer sidewalls then make them thicker while your doing your bulkheads Just one mans humble opinion

[Aswaff400]

what he said ^^^

 

[OldSkool67]

Glad to see the progress Craig!

Now is the worst part of it. Sounds and looks like you are on the right track.

[Capt Matt]

Moving right along
Remember you will need drain tubes thru the stringers/bulkheads so any water under the deck runs back to the bilge
Do you plan on removing the foam from the outer stringers too?

One of the big advantages of building your own grid/stringer system over the old set up is you gain lots of storage room in the floor along with the fact you can build the new stringers as high as needed to raise the floor. It also allows you to lay all new biaxle inside before sEtting stringers

Put your tank as far forward as you can start at the front of the console with back of the tank

Capt Matt

[CLM65]

Thanks Matt.  I should probably make a checklist so I don't forget those little details like drain tubes.

I will be removing the foam from the outer stringers as well.  I will be reusing the old stringers if possible.  Keeping costs down is key, and I think this is the most economical route.  But it does not leave much room for storage below deck, even with raising the deck a couple of inches, as you already know.  I can live with that.

And thanks for the tank location information.  I need to start laying out the modifications to my stringers, including the location of the tank.  I appreciate the guidance.

[Callyb]

I will be reusing the old stringers if possible.

I found one of those oscillating tools and an air hammer to be very useful in getting those stringers out in one piece. If I would have been able to reuse mine, I would have pulled them out with the foam still inside and cleaned them out upside down outside of the boat. It would save a bunch of glass work vs. cutting the tops open to get the foam out. I say that because you are going to need to build back to the original thickness where you make those cutouts.

I wish I had some pics to share, but I'm pretty bad about that...

[CLM65]

Thanks Carl.  As long as they are well bonded to the hull after I get all the foam out, I am not planning to remove the old stringers, except for part of the middle one so that I can get the wood out of the keel.  I will add glass to the inside of the stringers to add additional bonding between the stringers and hull.  I will also add more glass to the chines and the keel areas.

I assume you removed your stringers so that you can add more glass to the hull bottom?  While I'm sure that will make the boat stronger and is a good idea, I'm hoping the "good enough for the past 40+ years" adage holds true here.  I know members here have done it both ways, and I haven't heard of any boats falling apart yet   !

[gran398]

An old FB thread worth mention. The boys' done good:

viewtopic.php?f=2&t=5294

[gran398]

I'm hoping the "good enough for the past 40+ years" adage holds true here.  I know members here have done it both ways, and I haven't heard of any boats falling apart yet  <!-- s:roll: --><!-- s:roll: --> !

One thing to remember about this boat...she has never seen salt water. Which means she has never banged a five-footer in a head sea.

She was ordered up as a one-off in '67 from Hialeah and delivered to Lake Lanier, Georgia as a tender
http://classicaquasport.com/smf/index.php?topic=9672.0

The biggest swell she has ever seen is a pontoon wake  

 

[CLM65]

Thanks for that link Scott.  Another beautiful rebuild.  With 3 layers of 1808 on the bottom, that is one solid hull.

[CLM65]

It seems like forever, but I've finally got about 99% of the foam out.  I didn't find any stringer problems, and the entire stringer insert seems to still be well bonded to the hull .  I still have to remove the last remnants of foam and grind out the exposed original bonding putty, and prep the surfaces inside the stringers for some 1708 tabbing.  And also get a tank so I can determine how much of that center stringer to remove.



I also removed most of the inner transom skin to see what condition the wood is in.  The pic below shows the top of the inside of the transom.  It has about a 1.5" high solid fiberglass lip across it.  Do I just cut this top 1.5" off across the whole lower transom area?



It's a ways off, but I am going to need some guidance on filling in the area above the original outer skin (this will be an enclosed transom).  I've seen some people clamp a board to the outside surface and build it up from the outside in before the transom core gets installed.  And I've seen people add the transom core first, and then build up the outer skin from the inside out.  Is there a "preferred" or better way?

[CLM65]

A couple more questions for the experts....

I am getting close to ordering some material.  I was originally planning to go with vinylester resin.  However, it seems that the vinylester will cost about $100 more per 5 gallon bucket than the poly resin.  I see lots or rebuilds using poly, so I am rethinking this part and contemplating using poly resin.

My (inexperienced) gut feeling is that the poly will be fine for the deck, stringers, etc.  My biggest concern is the interface between the new fiberglass and the old, particularly where there is a butt-type joint.  For example, where the existing cap will be joined to the new transom cap enclosure, and where the outer transom skin will mate up with the new skin to make it an enclosed transom.  Since poly does not offer as strong a bond as vinyl, and is not as flexible as vinyl, and since these are high stress areas, I worry about the joint being weak and eventually developing some cracks.

Is there a problem with using both poly and vinylester resin?  Would the vinyl adhere to the poly without any issues?  I know epoxy will adhere to cured poly or vinyl resin, but I don't recall reading anything about vinyl over poly.  This approach would allow me to use poly on most of the project, and then vinyl only on the areas where I am concerned with the bond strength.

Thoughts?