Stringer Questions

The formula to figure out horsepower is.......length x width(widest point minus rub rails) x 2 x .5 for hard chines or x .8 for soft chines. Once you get that answer it's rounded to the nearest 5. Down most of the time.

 

You are indeed both right, they are just different stringers. One is a structural fiberglass stringer, and it does not matter what is inside, plenty of hollow ones around. The other is a wooden stringer and the fiberglass tabbing serves as a connection to the boats skin, all the forces are carried by the wood. Plenty around that do not even have fiberglass on top, only tape on the sides.

What2be, your transom has obvious rot spots around some of the bolts, whitout grinding them out you have no way of knowing how far it spreads. Icepick test is useless on fiberglassed ply, the core plys could be mush and the face solid. If the rot is still localized around the bolts you can scarf in dutchmens. The stringers also need opening up and at least reglueing of the cracks. The other option is to convert them to fiberglass stringers.

 

Thank you for clarifying that they were both right. it’s clear to me now. As for the ice pic test I tried it in the holes that were already in the transom that are used to attach some miscellaneous things that I had removed to make more room to work, The holes do not seem soft me so I was hopeful that I could simply remove the bolts were they didn’t use any aluminum backing and then grind through that area and see what kind of condition the wood is in and if it is OK simply add laminate on top of it and reinstall with a bracket this time. Obviously not the ideal repair method but I’m hoping will suffice For the next few years.

 

Well, what2be you have a lot to think about. You have an idea of what to do. Be careful about adding power or going to a four stroke. I don't know how practical it all is with that boat. A four stroke will weigh more and more power will cause more stress. Take time to think about what you might do. I've found that if I just ponder a problem for awhile, I save time and money in the long run. Good luck. MIA

 

Sorry I've been away longer than I thought.

MIA
What an amazing rebuild job.

There is a bit of a vocabulary issue. I would prefer to not call the solid wood stringer covered by little FG "cored"... But that's how they are commonly called.

Even Gerr would not consider a skin of less than .1 inch sufficiently engineered. These solid stringers are cheap and heavy. The FG is not considered in the caculations, it only holds the stringer to the hull (and the water in so they rot faster)

The stringers you built are lighter and more expensive to make. While the core is not considered in the stiffness caculations, it does hold the FG skins in alignment. Therefore I consider them to be core dependant.

To be totally independent from the core, the FG would have to be several times thicker. Making them heavy and doubly expensive.

Want2be

Deal with the transom issue first. Often theaft end of the stringers needs to be removed to accommodate the transom work. No need to repeat work.

Removing stringers is a messy nasty PIA chore. Use Gerr or a navel architect to get a layup schedule that goes right over the existing stringers. Making them core independent. The extra money spent on FG and epoxy will be saved from the chiropractor's bill.

 

"Nasty, messy, PIA chore". Absolutely right. Once I figured out the jig I relaxed a little because I knew I had a guide to follow for the engine beds. There was an older club member who knew what I was doing. He shows up one day with a box and says "You're going to need these. I saved them and figured someone would need them." Inside were a half a dozen Tyvek suits, boots and all. Thinking back the worst part was the goo. I remember having a five gallon jug of resin and slow hardener on one side of the hatch and all this fiberglass on the other. And lots of one quart mixing pots. The slow hardener helped a lot as I needed time to get things in place. I set them first with just a thin layer of 6 ox ounce cloth. Once the resin kicked and they were stable I pulled the jig and got busy with the layup. It was an all day affair. If I remember right there were five or six layers of 17/08 biaxle mat. If I had to do it again I think I would just use heavy cloth or roven woving and skip the mat as the mat really soaked up a lot of resin. But they're strong and they'll outlast me by a mile.

I didn't need chiropractic care but I was only 54. If I had to do them today I'd be living on pain killers.

MIA

 

Unless the timber inside the core of the stringer is securely bonded to the hull, and is in good condition, the timber is only acting as a former to give the shape of the stringer. Many boats are built with hollow 'top hat' section stringers - but this invariably needs a mould to create the stringers shape before they are installed and then overlaminated.
Even though MIA's Silverton was a production model, it was probably still easier (from a production efficiency point of view) to simply drop in some lengths of roughly shaped timber to act as formers, and then overlaminate them, rather than going to the expense of making a mould for top-hat fibreglass stringers, which would then still have to be overlaminated anyway. As the modern Plexus adhesives et al were not around in the early 70's when MIA's boat was built.

 

https://www.govinfo.gov/content/pkg/CFR-2002-title33-vol2/xml/CFR-2002-title33-vol2-sec183-53.xml

Here is the link for max hp rating.