Finally pulled the trigger on replacing the stringers on our Silver Nautique, been on the list for a decade.  I will post pictures over the winter, with the ambitious schedule to be done by late spring for skiing.

Over the weekend I pulled the seats and vinyl, dropped the rudder, pulled the shaft, removed the gas tank and other misc. stuff.  Had our boat mechanic pull the engine and store it.  Best $200 I’ve spent in a long time.  He thinks the motor is in good shape but will do a general review and a cylinder compression check while he has it.

My plan is to hang the boat to pick up most of the weight.  I’m also going to put supports under the two back corners and one support centered up front, just before the flat spot ends under the boat (just a bit in front of the fins) to keep things still while we work.  Those supports will also help me level the boat for the glass work.

I’ve been reviewing stringer materials and, of course, recommendations are all over the place.  I don’t think the bottom of the boat is really designed to flex, fiberglass is pretty rigid in plane and flexing the string encasements would crack them.  So I’m not worried about picking something flexible for the stringers.  

My second choice is white oak: strong, stiff, highly rot resistant and not very expensive. But oak is not dimensionally stable, it will expand and shrink a bit depending on moisture.  Yep, theoretically no moisture should get in there but, well, stuff happens… Same stability issue exists with most other solid wood choices (Douglas fir, etc.) 

My current first choice is Marine Ply, laminated together to get the right thickness, with staggered joints.  Will be stiff, soaks up penetrating epoxy well (unlike oak) to make it more rot resistant and is dimensionally stable moisture wise.  Forum thoughts on this are welcome.

Hung the boat from the lifting rings today.  Braced in the back corners and either side of the center just in front of the fins and drove some thin shims between the hull and the supports to take a touch of load off of the lifting rings.  

Easy enough to level it side to side.  Front to back was harder since nothing seems to match.  Decided to make the floor level, which put the existing aluminum engine support slightly out of level front to back compared to the floor but I doubt that matters much.

Deconstruction currently held up by the pylon.  I searched but couldn’t find any specific directions to remove the pylon beyond pulling the stainless bolt that goes through the bronze fitting at the hull and knocking out the lower pin that goes through the base of the pylon and tapping the pylon up with a hammer on a wooden block through the ring.  Not working, even though the pylon moves just at touch on the steel pin that connects the pylon to the bronze fitting.  Picture below.  Love to talk to the dude who though it a good idea to tie a bronze fitting to an aluminum post with a steel rod.

My next move is to put a post on either side of the boat, run a beam over them and put significant upward tension on the ring with a come along, heat the base of the pylon and tap up on the ring with a block of wood and a mall.  Any other ideas are welcome.

After tapping up on the pylon I noticed a touch of moisture around the base of the bronze fitting at the fiberglass hull which I don’t think was there before.  So I’m likely going to need to grind down around the fitting, see what’s going on and fiberglass things back together.  Anyone know exactly how the bronze fitting is set into the hull?  Picture below, but tough to see the moisture.

Sides of the boat are mostly prepped for glass to attach the floor.  This weekend I removed almost all of the stringers, still have the bottom inch or so of the main stringers to get out and a lot of grinding and sanding to do on the bottom of the hull.  The secondary stringer came out pretty much intact with just some rot in the tops so I can use them as templates.  The main stringers are attached hard to the bottom of the boat.  Probably going to need to splinter the rest out with a hammer and chisel.  Tops of the main stringers were trashed with rot.

I was able to create a detailed layout of the old stringers on paper so I went ahead and removed both sides.  I cut one side of the stringer fiberglass about 1” above the bottom of the boat to leave a lip and cut the other side flush with the bottom.  I will use the lip to locate the new stringers and I’m planning to use one of the 3M adhesive caulks to attach the stringer to the bottom of the boat and hold it still while I wrap them in glass.

Figuring the depth of the cuts in the stringer for the layout went a lot easier when it occurred to me to use one of the small laser levels we use on jobsites.  Set it on the 8” line I’ve already established, which was pretty accurate with the laser level, and then measured down to the stringer at each elevation change.

Also pulled the windshield.  I need to repair the blocking under the deck so the screws will take up, find a gasket to put between the deck and the windshield so we stop taking water when one of the kids buries the bow in the wake looping to pick someone up.  And find someone to powder coat the metal.

I have played around with foam in the hull... if you go with foam (closed cell type) try to keep the hard skin which forms on the outside of the foam as its less likely to soak up moisture.

I went with lining the area with DPC (Damp Proof Course Polythene) leaving plenty running over the sides to fold over the top to seal up once set.

After setting and sealing you can the lift the foam-covered blocks and any puckering of the DPC can be shrunk using a hot air gun, I went with a second covering of DPC and shrunk it over the first with the hot air gun and the blocks still fit back in the hull, that up to you.

The older hulls do let water through only by a very small amount, but over time/years it’s a problem, once you have finished the stringer work clean back the hull of all old coatings

and tank it all in epoxy resin 2 coats the second before the first is fully dry.

Moisture will always be in the hull just by temp changes its just keeping as low as you can.

Thanks for saving an old SN and keep the pictures coming good luck. roger. 

Removed the screws from the exhaust nipples and tried to tap them out with a hammer and block of wood but nothing moved.  I will try a heat gun next and see how things go.  Probably have another go at removing the pylon at the same time, working around it is a pain.

Grinding is mostly done but I’m sure there will be some touch up work once I get to installing the stringers and start concentrating on exactly how the fiberglass matts are going to lay.  I’m working up the layup schedule now using info from other stringer rebuilds.  Once I’ve got the schedule finalized, I will post it for comments.

Coosa Board has been delivered and I’ve set up an efficient cutting plan, won’t be much left after I’ve installed the stringers and deck. The secondary stringers where ¾” x 12’ and the mains where 1½” x 13’ so I’m going to lay up the secondaries out of three pieces of ¼” Coosa and the mains out of three pieces of ½”.  

Per some information from online, I will use a slightly thickened paste of resin to glue the Coosa together.  I’m going to use a vacuum bag technique to press the three layers of Coosa together for the stringers when I glue them up.  I have a vacuum pump that I picked up somewhere along the line so the rest of the vacuum bag setup only cost about $50 in fittings.  Sometimes we use HEPA negative air machines on our jobs, which require venting to outside the construction area so I have 6 mill plastic disposable ducting that comes flat in a 100’ roll.  Seems perfect for a vacuum bag to slide the stringers into.  Just cut the length I need, install the little hose fitting, slide the stringer in, seal the ends, suck out the air and squish.  What could possibly go wrong!

At first I leveled the boat using a 4’ level but I wanted the boat exactly level with no twist when I started epoxying in the stringers..  While trying to figure out a simple way to check for twist in the hull and level the stringers as I cut them to the shape of the hull, I remembered my laser level. The laser has a magnet hanger so I used some small hose clamps to attach a long steel bolt to the back davit hanger, you can see the level and the bolt in the picture.  I set the laser at 8” above the old floor level and rechecked the boat for level.  No surprise, it wasn’t exactly level and had a slight twist.  By the way, what points to measure for leveling front to back is a bit of a guess as the original floor definitely wasn’t flat.

I used the 4’ level and a long straight edge to check the sides, from side to side and the laser level to compare points on either side of the bottom working from back to front.  The boat is hung from the davit points but I’ve got supports under the back corners and the front roughly at the windshield to take some load off the davits points and stop the boat from rocking when I’m in it working.  I adjusted the davit hangers and shimmed the supports until I had the boat hull level by laser.  No matter how much I tried, if the hull was level side to side, the top of the sides, side to side just behind the windshield was a ¼” out by the 4’ level.  Back of the boat side to side at the top of the sides was level.  So the boat was built with a slight twist, not enough to matter and I elected to level the floor to the hull, not the sides.

Once the stingers where epoxied in I checked them with the laser.  Three where good at 8 ½” below the laser.  One secondary was correct in the back but was a ½” high by the time it got to the front.  15 minutes with a belt sander leveled it out to match the others.

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This is the stringer layout for my boat.  The old stringers where likely cut from a standard pattern but I’m not sure how tight they followed the pattern.  I expect each boat varies a little based on what I’ve seen on this boat.  Best if you use your stringers to layout your new stringers.  But if you can’t use your stringers, this should get you pretty close for boats like mine.

Top of the page is a plan view (looking down) of the secondary stringer, the space for the exhaust hose and the top of the main stringer.  The circles are bolt holes in the aluminum engine frame.

Below that is a side view of the stringer showing the dips, their locations and depths.  The gas tank is shown at + ½” because the floor is a ½” thick and the two aluminum angles under the tank sit basically flush with the top of the floor, making the bottom of the gas tank maybe a ¼” above the floor.  0” elevation is the underside of the floor.  Everything is measured from the transom of the boat in line with the thing you are laying out, keeping in mind that the main stringer hits the transom is a bit further aft than the secondary stringer because of the curve in the transom.

At the bottom of the page is a plan view of the secondary and main stringers showing the lamination schedule.  As you will see in a following post, the secondary stringer is made up of ¼” Coosa laminated together to get to ¾” thickness and the main stringer is made up of ½” Coosa to get to 1 ½” thickness.

EDIT:  In the above sketches I put the notches in the stringers to match the original, including the locations of the notches for the engine mount bolts (deepest notches on the sketch).  This was a mistake, the front engine mount bolt notches are much longer than needed and the back notches too tight.  I have way too much space on the front notches and I had to sand out and then re-glass the front part of the back notches to get a bit more clearance for those bolts.  In addition, the front of all the notches are sloped, for no reason I can discern.  Better plan is to make the notches run about 1 ½” past the bolt locations in the engine frame and make the ends of the notches vertical with rounded corners at the bottom and top of the vertical cuts.  

This is the floor layout plan using 4x8 sheets of Coosa or any 4x8 sheet material.  You can ignore the numbers at the top of the page, that’s just me trying to see how the side of the boat curves.  I templated the curve using a piece of heavy cardboard set to a line running down the center of the boat, marking, trimming with scissors, remarking and trimming till it fit neatly to the curve while the other edge of the cardboard stayed parallel to the boat center line.   The faint lines running parallel to the boat are the stringers.  Next post will show the cut schedule for the 4x8 sheets.

This is the Coosa Board cut plan.  Per this plan you need two ¼” x 4x8 sheets and four ½” x 4x8 sheets.  All the long skinny pieces are for the stringers.  The stringer pieces on the ¼” board are for the secondary stringers and they are 6” wide x 8’ or 6’ or 4’.  The stringer pieces on the ½” boards are the main stringers and they are 8” wide x 8’ or 5’ or 2’-6”.

The rest is pretty obvious, the only funky thing is I made the floor piece up under the bow by laminating two ¼” pieces together, otherwise you would need to buy another sheet to finish up.  If you are careful in your layout and cutting there will be plenty of small scraps left to make up the extra pieces next to the exhaust hoses, the little shelf on either side of the engine and the various other odds and ends, like the two roughly 11” x 14” pieces on either side of the gas tank.  

Dotted lines on the one piece are the cut out for the removable panel behind the engine. I would wait to cut that out till the final fitting of the floor pieces after everything under the floor is installed.  Side note: since the Coosa board is only a 1/2" thick, I added a 1" tall x 1/2" thick piece of scrap to the Coosa board that makes up the non-stringer side of the exhaust hose space.  I put it on the outboard side, the side closer to the secondary stringer. So the top of that piece is now 1" wide to give more landing space for the removable panel.  You can see it in one of my other pictures.  

To create the template for the bow floor, I set a thin straight piece of wood from battery box to point of the bow at the elevation of the floor then marked the side to side dimensions every 6”. I transferred that to a piece of cardboard to get close and then test fit and scribed lines on the cardboard till it fit neatly under the bow.  Transferred that to the Coosa, after a bunch of test fits and some sanding I got a nice fit for the Bow floor.   

Originally the wire harness, speed tubes, steering and throttle cables and the bilge pump tube all ran in one pipe from engine to the bow.  I’ve broken those into individual pipe chases for ease of repairs in the future, creating the need for some creative pipe bending using heat.  And lots of different holes in the bow floor and that bulkhead behind the battery box.  The steering cable has a 16” stainless bar on the end so the 2” pipe has two very light bends in it so the pipe can turn up through the bow floor and still allow the bar to slide through.

At this point, all the flooring is cut and fit.  With all the Coosa in place, I have a nice flat floor with only the pylon interrupting it. Next step is to test fit the carpet I bought while nothing is in the way.

Bought 8’-6” wide carpet and tested it in the boat today.  Not ready to install, still need to finish epoxying the floor down and install the foam.  I was worried the 8’-6” wide carpet wouldn’t be wide enough to run up the sides but that turned out fine.  I was hoping to be able to wrap the carpet up the sides without cutting.  I think that would work starting at the back and getting about halfway to the front of the boat but after that the curve and flair of the side is going to create folds, so that plan is out.  I’m going to have to cut it at the floor to side transition like was done originally.  

I was going to trim the carpet to fit today but I think it will work better if I glue the carpet down to maybe 6” from the sides, leave the last 6” loose and then cut it at the floor to side transition.  Nothing moves during or after the cutting that way.  

The original carpet trim strips are definitely not made for a 90 degree turn up the sides, CC just kind of made it work.  If I reuse them I think I need to actually turn the side carpet out onto the floor a half inch or so to get it under the trim strip so the carpet doesn’t ravel.  The floor carpet then slips into the trim on the other side.  Does anyone have a source for a carpet trim strip that’s designed for a floor to side transition?  Seems like a normal detail and there should be a trim piece for the 90 degree transition.