79 ski nautique stringer replacement

Hello all,

It's John here with the 79 Ski Nautique back for some more advice.

I had a scare last summer when my driveshaft detached from my coupler, and after some digging we found my engine was out of alignment. Here is a link to that post. I checked my alignment regularly for the rest of the season, and no matter what I did, I could not keep the engine in alignment. Near the end of the season I finally realized my problem:

The stringers have started to rot where the engine mount bolts are, and the engine doesn't stay put anymore. If I try to tighten these bolts they just spin in place. I pulled the boat out, winterized it, and put it away for the season, knowing I would need to replace the stringers before I can keep using it.

That's my task this spring. I removed the seats, seat mounts, fuel tank, rear floorboard. Then I pulled out the engine using an automotive engine hoist. I took out the carpets, then removed all the items that I could from the engine bay (fuel filter, trans oil cooler, bilge pump, etc). Here is a before and after:

Here's where I'm a little stuck. I would like to remove the floor but leave the old stringers intact so that I can take precise measurements of them, but there's no way to remove the floor without grinding it out, and that will destroy the old stringers.

How would you all proceed from here? My best plan right now is to measure the exact location of the engine mount points and ski pole relative to the hull and the transom, then just cut everything out and rebuild it following wayoutthere's excellent walk through, with some adjustments.

Some info on the boat - I bought it last year from the original owner who owned it since it was new in 1980. Somewhere in the boat's lifetime it had the stringers replaced and got a new (same model) engine. So I'm trying to figure out what is original CC design and what is the original owner's rebuild. I'll post an album with some more photos here shortly.

Thanks in advance,

John

Thank you all so much for the replies!

Keno, do you really think it is a PCM? The original owner said that the second engine was the exact same model as the first (although the more I learn about this boat the less I trust the original owner ). It has Commander casted into all the mounts (if you look closely at the first picture Commander is casted into the mounts that support the engine body), although I can't find anything specific casted into the engine body itself. The exhaust risers are definitely PCM. Is there someone on the engine body that I should expect to find an identifier?

Wayoutthere,

These photos are an excellent resource, thank you! I took as many measurements as I could above the carpet as well as below it. Now I'll try to carefully remove the floor so I can get some good measurements of the outboard stringers as well.

Everything mounted above the carpet:

Everything below the carpet:

Here are a couple of Commander 351's for comparison.

The locations of the water pump and alternator are original and you can see the original thermostat housing too.

The second picture has a missing belt, a missing hose and a disconnected hose 

Also your buddy has an 80's 2001 (82 through 89 were the 2001 years)  

It also adds maybe a little sound deadening

It also kept the USCG happy

A small spade type shovel works good for getting it out

Like mentioned earlier the PCM stuff may have been due to manifold issues and/or parts availability of the Commander stuff.

It's been out of production for a long time and the Commander specific parts have been hard to find for a long time. PCM 351w things like  thermostat housings and covers and timing covers are hard to find these days even with PCM still being alive and well.

The only number in my manual is for a Power House Marine located at 4760 NW 128th Street Miami, FL. Looks like it has since moved or gone out of business though.

May help with your build sizes are mm taken from the wide side or facing the centre of the hull, for Mk2 SN 

Thanks for saving the boat.

Making progress, slow but steady. You all weren't kidding about how time consuming this job is.

I found the previous owner's "stringer repair", which looks like they just poured epoxy into an already half rotten board.

That was a pain to remove. I cut out the first stringer with a reciprocating saw, which was a mistake. The better way to do it is to use an angle grinder with a cutting wheel, and just cut through the fiberglass as close to the base of the hull as possible. With a clean cut through the fiberglass all the way down on both sides, I could pry the old stringer out with a crow bar. It helped that my stringer was completely rotten. With the wood from the stringer out of the way, a grinding wheel on the angle grinder can remove the stubs that remain.

I'm starting to think about the rebuild now and have a few questions. I read on this forum that Douglas Fir is the lumber I want for the stringers, but I called around to the local lumber supply stores here and no one seems to carry it. They said they carry 'SPF'. Is 'SPF' close enough for this job?

Would it be a bad idea to skip the foam on the rebuild? I'm thinking the space in the bow that used to be all foam could instead be the battery compartment, a storage for a ski, a watertight glove compartment. and a spot for a cooler.

Hello all,

It has been a slow month but im finally starting to make progress again. Everywhere that is going to get glass or gel coat has been grinded and sanded, and now I'm making the new stringers.

Unfortunately I could not find anyone within 500 miles who could supply fir boards, and I had no luck finding cypress either. After weeks of searching I decided to go with cedar. Not ideal but I thought it was better than southern yellow pine or SPF. I have the bottoms of the boards cut nicely to fit the hull, and now I have to shape the tops. This leads to my question:

In this diagram, the tops of the stringers are cut down 46cm from the top where the engine mounts will sit.

My old stringers also had this indentation. Why then do the engine mounts sit on these wooden blocks?

Would it be better to leave out the wooden blocks, and just shape the tops of the stringers so that they are correct height off the hull where the engine mounts will be? Or is there a purpose for the wooden blocks?

Thanks in advance,

-John

  IS DOUGLAS FIR STRONGER THAN SOUTHERN YELLOW PINE?

1708 is great stuff, it needs thin resin for fast and thorough wet out, it also needs approx 32 ounces of resin per 1296 sq inches of material.

You'll need fast wet, good pot life and working time. Vynil-ester or epoxy and a solid plan will give you the results your after.

Post your stringer dimensions length and height and how much tab you plan to have  from stringer onto the hull i'll work a mock up of how i was told to install stringers and take a pic.

wayoutthere,

Thanks for your post. This is great information, and is pretty much how I was planning it in my head but its good to see some pictures. I was planning to use a router to put 1/8" or 1/4" rounded edges on all the stringer tops and try to go up over and back down with a single piece. I'll have to report back whether that's feasible or not.  Unfortunately I already ordered all the fiberglass a couple of weeks ago, so I already have the poly resin. The folks at fiberglass supply depot said they'd done this job a few times and that epoxy was overkill, so I took their advice. I suppose I'll find out for myself whether they're right.