Converting to Foam core stringers and transom from original wood affect the ride?

[Hugo G K]

Hi I have been studying seacrafts for a while now and finally decided to take on my own restoration project on a 1968 20 seacraft. With no surprise, when I removed the deck I found the wood in the stringers and transom have started to rot. I have decided to replace the wood with a foam core and fiberglass which will obviously reduce the overall weight. My Question is, by reducing so much weight by switching from wood to foam, would this affect the ride of the boat? If so for the better or worst? I am also adding a flotation bracket and closing up the transom.....
Please let me know your thoughts and suggestions,

Thanks

[Bushwacker]

Moesly used wood stringers in the old 21, but I think he was using all glass stringers by the time he built the 19' Bowrider in '64 or '65, and then the 20 cc in about '67 or '68. I know for sure that all the Seafari's had glass stringers starting in '69, and it's the same basic hull as the cc model. The construction/laminate schedule is outlined in this magazine article, http://www.classicseacraft.com/broch...cle/index.html. The last page contains a sketch that shows how the pre-molded stringers were installed, about half way through the layup. I think Potter may have filled the stringers with foam in his boats, but I believe the Moesly boats like yours have hollow stringers. The only stringer with wood in it is the keelson, and even in it the glass provides most of the stiffness. I believe website founder Trader replaced his keelson with half of a PVC pipe that was glassed over but left hollow for drainage. The I/O's did have wood for the engine beds attached to the stringers, but I think most of the stringers were glass, except for the 21, and even those were covered with glass. Like any beam in bending, most of the strength/stiffness is provided by the outer fibers.

You may find that the boat is full of wet foam between the stringers, so removal/replacement of that would save a lot of weight. Reducing weight in the transom by going to a composite core is a good thing, especially if you intend to install a bracket. In fact, the issue of wood vs. foam in the stringers/transom is a NIT compared to the installation of the bracket in terms of how it will hurt the ride! Been there, done that!

A bracket will shift the boat's CG aft by a fair amount, so you need to be very careful with that. These boats were designed for the largest outboards available in the mid-60's, which weighed 250-300 lbs. Most of the new 4 cyl 4-strokes are in the 400-500 lb range and that's almost too heavy for good balance, even if you just hang it on the transom! Adding a bracket only makes it worse. Use the lightest motor you can find (probably a 2-stroke), and use the smallest possible setback to minimize the CG shift. Consider moving the fuel tank and CC forward to offset the weight of the motor shifted aft. To maintain self-bailing capability, go with a bracket with the largest possible flotation tank (a Hermco) and consider raising the deck a couple of inches. Don Herman said he can build his brackets with different amounts of setback, I believe 18", 24" and 30".

The 20' SeaCraft as originally designed will plane at 12-13 mph, which I think is a very important capability! The boat is light enough to go completely airborne at about 20 kts in seas over 3', so being able to hang on plane at low speed when it gets rough is a big deal to me. My boat would do that when I had a 300 lb motor on the transom, but it took a lot of tweaking to get back there after installing a new and much heavier motor on a bracket! Hope this helps. Denny

[McGillicuddy]

Originally Posted by Hugo G K

Hi I have been studying seacrafts for a while now and finally decided to take on my own restoration project on a 1968 20 seacraft. With no surprise, when I removed the deck I found the wood in the stringers and transom have started to rot. I have decided to replace the wood with a foam core and fiberglass which will obviously reduce the overall weight. My Question is, by reducing so much weight by switching from wood to foam, would this affect the ride of the boat? If so for the better or worst? I am also adding a flotation bracket and closing up the transom.....
Please let me know your thoughts and suggestions,

Thanks

Very interesting. Could you post som pictures of your project and the stringers grid? Very interested in the keelson, too, as its presumably wood. Is it rotted too?

[Hugo G K]

Wow thanks so much for replying so quickly and with such good information!

After reading the replies it made it clear that there is still a lot about my specific SC that I need to learn. Although I did leave out a lot of valuable info that I should have mentioned in the first post.
The title on the boat reads 1968 length 19 and Propul INBRD.. Since then the boat has been converted to an outboard and when I asked the seller, he claims he had bought the boat as he sold it and could not offer any additional history. I became curious so I was able to contact Carla Moesly (Daughter) and had sent her pictures of the boat. She was a little unsure herself but suggest that it could have been a bow rider converted to a CC. The deck on the boat was in bad shape so I decided to begin the restoration process and rip out the deck which is basically where I am now. The guy I have doing most of the work pointed out the condition of the stringers and suggested they needed to be filled in with foam for the core. After reading your reply Bushwacker, I did notice some stringers were hallow and if I recall correctly, there was one stringer that had wood as the core. I figured the hallow stringers probably had wood but rotted over time. As far as the transom, the wood is definitely rotting and needs to be replaced. But if you say this was normal for the stringers to be hallow then I will definitely question the work.
Tomorrow I will go to the boat and examine the stringers much more closely. In the mean time I figured I would try to put up some pictures I have just in case maybe you guys can give me some more good input on what I actually have and what you suggest I do with it.

Thanks Again,

Hugo G K

Copy and paste the website below in your URL to see the pics.

http://www.flickr.com/photos/88052914@N05/

[Bushwacker]

Hugo, if it really was a 19 Bowrider originally, that would explain some wood in the stringers. This article from a 1966 Boating magazine test http://www.moeslyseacraft.com/upload...oating-6pp.jpg on Carla's Moesly SeaCraft website (a great website you should check out if you haven't already done so!) indicates that spruce was used in the stringers. Carl also used spruce for the 21 stringers because of it's light weight. I knew he used a grid system for stringers and bulkheads in the Bowrider, but he evidently didn't start using the premolded hollow stringers until he started building the 20's, which also included a separate inner liner that was bonded to the top of the stringers. He once told me that even if the wood rotted out it wouldn't matter because there is so much strength in the glass wrapped over the stringers. Not much was known about fiberglass in the early 60's, so his approach was to build the boats as light as he thought he could get away with, and then go beat the hell out of it in the ocean races and beef up anything that broke. SeaCrafts absolutely dominated the outboard offshore powerboat classes in the mid 60's and nothing ever broke despite racing in some extremely rough seas, so Carl definitely knows what he's talking about!

Just make sure the glass around the stringers is in good shape and that none of the bulkheads were removed during the CC conversion! When the deck is bonded to the top of the stringers, it basically creates a big I-beam with 4 vertical ribs that is extremely stiff. I'd recommend using epoxy resin to maximize the bond strength with the old polyester. The 19 hull is basically identical to the 20 below the chines, but it doesn't have as much flair or the 1" wide flat at the chines in the forward sections, so it tends to be a bit wet in a chop. You might want to consider adding some spray rails at the chines. Carla's husband Skip (alias Old Timer) can give you some info on a spray rail design for the Bowrider. Denny

[Islandtrader]

On my 21 one of the main stringers rotted out due to water intrusion. The glass on the stringer was still good. So I just added more glass and it is very stiff. Like Denny stated, wood or foam is only to give shape.

Check out page 3 of my rebuild...somewhere in #60 and you will see that I just glassed over the existing stringer. This is called the lost mold process.

[Hugo G K]

Thanks again for all the helpful information! I will be following up with you guys throughout the project and will let you know when I run into more bumps...

Cheers!

Hugo