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jimithing posted 01-07-2003 11:21 AM ET (US)
have the bench seating mounted on top of the risers and both are beginning to show signs of splitting. What's the best way to prevent this from happening again since I plan on replacing them? A floor brace at the center of each? Rather not have to screw into the decking.
All comments are welcome. Thanks.
Tom W Clark posted 01-07-2003 11:46 AM ET (US)
What boat? Factory thwart or a replacement?
jimithing posted 01-07-2003 11:49 AM ET (US)
Thanks Tom:
Failed to mention the most important part:
15SS
All replacement wood done to my specs.....more of a sport interior but with the SS wraparound railing
Tom W Clark posted 01-07-2003 11:54 AM ET (US)
You could use the seat back option from the Sport's. The wrap around rail would insert into the second Tee of your existing rail (there's a "hot dog" or 4" length of 3/4" tubingint here as a splice). This is how the wrap around rails are installed on the Sport models.
Or, you could build the seat back from the Super Sport.
jimithing posted 01-07-2003 11:54 AM ET (US)
rather a supersport 15
Tom W Clark posted 01-07-2003 12:00 PM ET (US)
Sorry.
If the thwart seat is sitting on top of the riser, then maybe there needs to be a knee brace under it to keep the risers from rocking from side to side and working the screws.
The thwart seat itself needs to be not only 1" thick (not 3/4") but the board selected should have the grain oriented relatively vertically so it will bend less. At the factory back when Whaler was still making their own wood parts, they would put a load on each and every thwart seat to see if it was stiff enough to survive.
AnthonyT posted 01-07-2003 03:03 PM ET (US)
Are the cracks the result of load stress or possibly due to expansion and contraction of wood that is constrained ? What type of wood was used and how is it joined/secured to other cross grain ?
jimithing posted 01-08-2003 10:23 AM ET (US)
Thanks for all the replys. very helpful.
the bench that is splitting is mounted, with screws, atop the risers that are screwed into the gunnels. The risers as far as I can tell do not flex. The bench was salvaged from the original supersport interior, milled, due to severe weathering to about 3/4 inches, finished and used for this new interior.
I hit a large wave and heard a pop.....voila....noticed the wood splitting from back to front across the grain.
Bracing it to the decking seems to be the best idea.....How can I do that without screwing into the deck....is there a particluar adhesive I should use?
jimithing posted 01-08-2003 10:25 AM ET (US)
as far as the seat back option...would that be sturdy enough to prevent this from happening again.....?
Where can I get the seatback option for an 87 15?
minimontauk posted 01-09-2003 07:54 PM ET (US)
Jimthing:
Sounds like we have the same boat, an 87' 15'. Mine is a Sport CC. The previous owner put in an aftermarket cooler seat. I still have the wrap around seatback rail, but am missing the brackets that curve down to support the seat. CMI has a railing diagram for this, which they faxed me. They can fabricate exact replacements for OEM Whaler railings. I may eventually restore the original seatback setup, if I can find some dimensioned plans. As far as supporting the seat, I plan to use the original bench as a thwart seat in front of the console. I am making new side rails to support it. I am planning on making a mahogany center support screwed and glued to the seat bottom, with rubber or teflon furniture pad feet to bear on the deck. This will give me the support without screwing into the deck.
Cicada posted 01-10-2003 12:20 AM ET (US)
Minimontauk,
Are you looking for dimensioned plans for the wood? I have a '78 15 Sport with the seatback option. All of the wood is out of the boat and I am in the process of preparing drawings prior to refinishing. I don't know if this is the same setup.
An example of the relevance of grain. The front thwart seat has a pretty good cup in it from the grain orientation. To plane the seat until it was flat would make it too thin for proper support and wouldn't fit properly under the rubber spacers inleted into the sides. I need to make a decision to replace or refinish with the cup. Probably keep the seat with the cup. Put the cup up and it's stronger, put the cup down and it's a little more comfortable.
Paul
skred posted 01-10-2003 08:06 AM ET (US)
Prior to my 15, I had a 13 with a thwart seat "immininent failure". I fashioned a 3/4" mahogany vertical brace that was full seat width at the top but matched the console side curve, so the bottom (where it met the deck) had a smaller "footprint". I screwed 2 attachment strips on the underside of the seat in the center, leaving a slot for the vertical brace, screwed the brace to the strips, put two 1/2" rubber pads on the bottom edge of the brace, and did not fasten the bottom of the brace to the deck. It just rests there. With the proper fit (very tight), the brace has never moved left or right, and offers excellent support for the thwart seat. It looks quite "original" - though there was no such brace on a Whaler. Inexpensive and easy solution....
whalersailer posted 01-10-2003 05:45 PM ET (US)
jimithing,
It sounds like the root of this failure is the removal of 1/4" (25%) of the thickness of the seats. The mechanics of beam bending stresses are such that the strength of the beam (seat in this case) is inversely proportional to the CUBE of the thickness of the beam. Therefore, by shaving just 1/4" off of the 1" original thickness, the strength was reduced by 2.37 times. In other words, the 3/4" seat can only support 42% of the load that the 1" seat can support.
Now that the numbers are out of the way, I would suggest following Tom's suggestion of making the new seats AT LEAST 1" thick. If you are really concerned about it, make them 1-1/4" thick and call it good. Better yet, you could make a laminate of a 1" board (seat top) epoxied to a slightly smaller (x-y) .25" board on the bottom. If executed properly, this would actually be stronger than the 1.25" board.
Hopefully this sheds some light on the situation. The new seats don't have to be much (if any) different than the stock ones, and you can keep the boat looking the way she does now.
Good luck!
-WS
lhg posted 01-10-2003 06:27 PM ET (US)
I agree that planing the seat down to 3/4" is the problem. If this board is to remain, a vertical leg, only attached to the seat underside, can be installed midship, and it need not be fastened to the floor.
minimontauk posted 01-10-2003 08:13 PM ET (US)
Cicada:
I would be real interested in plans for the seatback option. Can I send you a SASE for copies once you draw them up? Or you could e-mail me. I'd appreciate it.

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Author	Topic: bench seating splitting under stress
jimithing	posted 01-07-2003 11:21 AM ET (US) have the bench seating mounted on top of the risers and both are beginning to show signs of splitting. What's the best way to prevent this from happening again since I plan on replacing them? A floor brace at the center of each? Rather not have to screw into the decking. All comments are welcome. Thanks.
Tom W Clark	posted 01-07-2003 11:46 AM ET (US) What boat? Factory thwart or a replacement?
jimithing	posted 01-07-2003 11:49 AM ET (US) Thanks Tom: Failed to mention the most important part: 15SS All replacement wood done to my specs.....more of a sport interior but with the SS wraparound railing
Tom W Clark	posted 01-07-2003 11:54 AM ET (US) You could use the seat back option from the Sport's. The wrap around rail would insert into the second Tee of your existing rail (there's a "hot dog" or 4" length of 3/4" tubingint here as a splice). This is how the wrap around rails are installed on the Sport models. Or, you could build the seat back from the Super Sport.
jimithing	posted 01-07-2003 11:54 AM ET (US) rather a supersport 15
Tom W Clark	posted 01-07-2003 12:00 PM ET (US) Sorry. If the thwart seat is sitting on top of the riser, then maybe there needs to be a knee brace under it to keep the risers from rocking from side to side and working the screws. The thwart seat itself needs to be not only 1" thick (not 3/4") but the board selected should have the grain oriented relatively vertically so it will bend less. At the factory back when Whaler was still making their own wood parts, they would put a load on each and every thwart seat to see if it was stiff enough to survive.
AnthonyT	posted 01-07-2003 03:03 PM ET (US) Are the cracks the result of load stress or possibly due to expansion and contraction of wood that is constrained ? What type of wood was used and how is it joined/secured to other cross grain ?
jimithing	posted 01-08-2003 10:23 AM ET (US) Thanks for all the replys. very helpful. the bench that is splitting is mounted, with screws, atop the risers that are screwed into the gunnels. The risers as far as I can tell do not flex. The bench was salvaged from the original supersport interior, milled, due to severe weathering to about 3/4 inches, finished and used for this new interior. I hit a large wave and heard a pop.....voila....noticed the wood splitting from back to front across the grain. Bracing it to the decking seems to be the best idea.....How can I do that without screwing into the deck....is there a particluar adhesive I should use?
jimithing	posted 01-08-2003 10:25 AM ET (US) as far as the seat back option...would that be sturdy enough to prevent this from happening again.....? Where can I get the seatback option for an 87 15?
minimontauk	posted 01-09-2003 07:54 PM ET (US) Jimthing: Sounds like we have the same boat, an 87' 15'. Mine is a Sport CC. The previous owner put in an aftermarket cooler seat. I still have the wrap around seatback rail, but am missing the brackets that curve down to support the seat. CMI has a railing diagram for this, which they faxed me. They can fabricate exact replacements for OEM Whaler railings. I may eventually restore the original seatback setup, if I can find some dimensioned plans. As far as supporting the seat, I plan to use the original bench as a thwart seat in front of the console. I am making new side rails to support it. I am planning on making a mahogany center support screwed and glued to the seat bottom, with rubber or teflon furniture pad feet to bear on the deck. This will give me the support without screwing into the deck.
Cicada	posted 01-10-2003 12:20 AM ET (US) Minimontauk, Are you looking for dimensioned plans for the wood? I have a '78 15 Sport with the seatback option. All of the wood is out of the boat and I am in the process of preparing drawings prior to refinishing. I don't know if this is the same setup. An example of the relevance of grain. The front thwart seat has a pretty good cup in it from the grain orientation. To plane the seat until it was flat would make it too thin for proper support and wouldn't fit properly under the rubber spacers inleted into the sides. I need to make a decision to replace or refinish with the cup. Probably keep the seat with the cup. Put the cup up and it's stronger, put the cup down and it's a little more comfortable. Paul
skred	posted 01-10-2003 08:06 AM ET (US) Prior to my 15, I had a 13 with a thwart seat "immininent failure". I fashioned a 3/4" mahogany vertical brace that was full seat width at the top but matched the console side curve, so the bottom (where it met the deck) had a smaller "footprint". I screwed 2 attachment strips on the underside of the seat in the center, leaving a slot for the vertical brace, screwed the brace to the strips, put two 1/2" rubber pads on the bottom edge of the brace, and did not fasten the bottom of the brace to the deck. It just rests there. With the proper fit (very tight), the brace has never moved left or right, and offers excellent support for the thwart seat. It looks quite "original" - though there was no such brace on a Whaler. Inexpensive and easy solution....
whalersailer	posted 01-10-2003 05:45 PM ET (US) jimithing, It sounds like the root of this failure is the removal of 1/4" (25%) of the thickness of the seats. The mechanics of beam bending stresses are such that the strength of the beam (seat in this case) is inversely proportional to the CUBE of the thickness of the beam. Therefore, by shaving just 1/4" off of the 1" original thickness, the strength was reduced by 2.37 times. In other words, the 3/4" seat can only support 42% of the load that the 1" seat can support. Now that the numbers are out of the way, I would suggest following Tom's suggestion of making the new seats AT LEAST 1" thick. If you are really concerned about it, make them 1-1/4" thick and call it good. Better yet, you could make a laminate of a 1" board (seat top) epoxied to a slightly smaller (x-y) .25" board on the bottom. If executed properly, this would actually be stronger than the 1.25" board. Hopefully this sheds some light on the situation. The new seats don't have to be much (if any) different than the stock ones, and you can keep the boat looking the way she does now. Good luck! -WS
lhg	posted 01-10-2003 06:27 PM ET (US) I agree that planing the seat down to 3/4" is the problem. If this board is to remain, a vertical leg, only attached to the seat underside, can be installed midship, and it need not be fastened to the floor.
minimontauk	posted 01-10-2003 08:13 PM ET (US) Cicada: I would be real interested in plans for the seatback option. Can I send you a SASE for copies once you draw them up? Or you could e-mail me. I'd appreciate it.