Sport 13: Moving Thwart Seat To Affect Performance

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Author Topic:   Sport 13: Moving Thwart Seat To Affect Performance

teleman360 posted 01-20-2007 04:09 PM ET (US)
While reinstalling my newly finished wood interior [on my 1973 classic Boston Whaler SPORT 13], I noticed there where two sets of holes for the seat clamps and an extra screw, with washer, in the deck under the side console. I determined that when I took the wood out, the holes further back had been used. I then reinstalled the wood in the same location. Later this got me thinking about weight distribution and performance of the boat. The difference is only 4- inches, but I have a hard time fitting a standard 6.5-gallon gas tank behind the seat. It has me thinking it would it be easier to plane off with our weight 4-inches further. So, do people here think it is worth my time, perhaps a new steering cable, and extending my wiring to move everything forward? How will this affect performance? Thanks!
Binkie posted 01-20-2007 06:32 PM ET (US)
That`s a good question, and when my restoration is complete, my console will be 4" forward of the original location. I believe that the boat will ride better, but it is only my assumption. What bothers me is I`m sure different locations were tested when these boats were designed.
Rich
Tom Hemphill posted 01-22-2007 07:01 AM ET (US)
Moving everything forward four inches sounds like a good idea to me. My 1966 13-foot is apart for wood restoration so now's a good time to do it. My Teleflex steering cable is a little long anyway, and my kids are grown up so I'm less likely to have ballast forward. 25 horsepower motors were typical when my boat was designed; the engineers may have done things differently given the heavier motors we tend to run nowadays.
13sport posted 01-22-2007 03:44 PM ET (US)
What will you do with the side rails? On my 1976 13' sport moving the thwarts 4 inches forward would conflict with attaching the bottom of the side rail into the the wood that is embedded into the hull.
Sport
Boatplans posted 01-22-2007 05:15 PM ET (US)
The further aft the weight, the faster the boat. There will also be a greater tendancy to porpoise as weight is shifted aft. It depends on the load. One passenger forward cancels out any problems with planing off or porpoising.
Because the fuel tank should be as far aft as possible, the seat cannot be further after than up against the side of the 6 gallon tank. Place the tank on side opposite the pilot. You will still need a tiller extension.
With a pedistal and wheel, the location of wooden backup in the hull determines the location of the seats.
Binkie posted 01-22-2007 05:49 PM ET (US)
With the entire interior moved four inches forward, you could build a nice 12"high fold down seat back for the rear seat, and your passenger could ride in the rear seat also,and be more comfortable. With today's heavier outboards I think the boat would ride much better. If you get an under seat fuel tank, you could test the boat, and see if it would be better riding under the front or rear seat. 13 ft. Whalers with their hooked bottom won`t go fast anyhow, so why bother trying to set it up for speed. As far as looking for embedded wood to screw your mahogany clamps and console too. There are other alternatives to this that work just as well.
Rich
teleman360 posted 01-22-2007 10:02 PM ET (US)
I messured today and the entire interier was moved back 6". I tried moving it forward, but I will have to get a new steering cable to do this. If I come across a good price for a 10' cable I think I will go ahead and move it. As a side, my OB is a Johnson 28 which weighs 115 lbs. much lighter then todays new OB's.
Boatplans posted 01-23-2007 12:18 AM ET (US)
In most cases, Boston Whaler 13 footers should keep the weight and balance established by the builder, the way the boat was set up when delivered from the factory.
Binkie posted 01-23-2007 07:05 AM ET (US)
boatplans
The weight of a late `50`s 25hp motor was just slightly over one hundred pounds. I believe modern motors with the additional weight, make is necessary to experiment, with driver and passenger locations.
Rich
13sport posted 01-23-2007 12:06 PM ET (US)
How about a genuine certified engineer weighing in on this discussion? I would also like to know what Clark Roberts thinks of moving the stock interior forward.
What about those who have converted a 13' to a center console. Did you move the center of gravity forward?
I am think of re-powering with a 210lb four stroke. I am looking at all of the options of maintaining the current static trim. Moving the interior forward is a option that I haven't thought about.
Sport
Boatplans posted 01-27-2007 05:28 AM ET (US)
Binke, You make a good point. When it comes to a heavy 4 cycle outboard, hydraulic tilt and trim should help. Securing a 12 gallon tank under a seat precludes shifting conventional 6 gallon tanks as needed to trim the boat.
Tom Hemphill posted 07-22-2007 12:13 PM ET (US)
This is to follow up on my expressed interest in moving the interior forward a little. From screw hole evidence, it looks like mine had already been moved forward 2 inches. I was able to go forward an additional 3 inches and still attach the base of the console to embedded wood under the deck. (Thanks, CW, for providing the wood locating drawing.) Yes, I'll have to relocate my side rails forward, but there should be hidden wood there, too.
The front of the console is now 63 inches from the inner transom. I believe the distance between the thwarts is as originally built. I have 22 inches behind the aft thwart, possibly enough room to build a small storage compartment and backrest. My 6-gallon gas tank and battery continue to live in the stern.
The change in performance is minor, but suits my needs. With one aboard, it gets on plane extremely easily (~ 10 MPH) and goes plenty fast for me (around 30 MPH) when I want, while retaining very stable handling. Power tilt and trim would be nice, but I don't want the added weight, cost and complexity.
My 1987 35-HP Mecury weighs around 200 pounds. I think if such a motor had been standard-issue in 1966, the interior would have been located as mine is now. I feel I have a very predictable and safe skiff which handles a variety of tasks competently.
renoduckman posted 07-22-2007 07:20 PM ET (US)
I had a 72 13ft for 13 years. It was a tiller boat. But one thing i do know that it was rear heavy for sure. It had the wood seat move forward and we considered moving it even more. I kept the 6 gallon Merc tanks in front of the seat. Seemed to me it had a better ride with 2 people and gear near the bow. I think id experiment with it for sure. Test first.
Binkie posted 07-22-2007 07:21 PM ET (US)
Tom,
I`m happy that moving the interior on your 13 footer worked out for you, and you didn`t find any negatives. Its possible you may have lost a minuscule of performance, but easier planing and minimal to no porpoising will more than make up for it. Does the boat seem wetter, and does the bow ride lower when at speed?
My 13 footer is two or three weeks away from a water test. I moved the custom side console interior about five or six inches forward. The console is much larger than original. The rear thwart is raised 4", 2, 6 gallon tanks and the battery sit under the rear thwart, I built a 32lb, 23" wide,teak rear casting platform,behind the rear thwart. The outboard is a `58, 35hp Evinrude Lark which is a lightweight by todays standards.
Rich
Tom Hemphill posted 07-22-2007 09:05 PM ET (US)
I would say that yes, the bow is a little lower at speed. I expect that it would be wetter as a result, but my testing thusfar has been on quite flat water. In the ocean I might trim the motor out one notch. (It's now using the middle of five possible trim positions.)

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Author	Topic: Sport 13: Moving Thwart Seat To Affect Performance
teleman360	posted 01-20-2007 04:09 PM ET (US) While reinstalling my newly finished wood interior [on my 1973 classic Boston Whaler SPORT 13], I noticed there where two sets of holes for the seat clamps and an extra screw, with washer, in the deck under the side console. I determined that when I took the wood out, the holes further back had been used. I then reinstalled the wood in the same location. Later this got me thinking about weight distribution and performance of the boat. The difference is only 4- inches, but I have a hard time fitting a standard 6.5-gallon gas tank behind the seat. It has me thinking it would it be easier to plane off with our weight 4-inches further. So, do people here think it is worth my time, perhaps a new steering cable, and extending my wiring to move everything forward? How will this affect performance? Thanks!
Binkie	posted 01-20-2007 06:32 PM ET (US) That`s a good question, and when my restoration is complete, my console will be 4" forward of the original location. I believe that the boat will ride better, but it is only my assumption. What bothers me is I`m sure different locations were tested when these boats were designed. Rich
Tom Hemphill	posted 01-22-2007 07:01 AM ET (US) Moving everything forward four inches sounds like a good idea to me. My 1966 13-foot is apart for wood restoration so now's a good time to do it. My Teleflex steering cable is a little long anyway, and my kids are grown up so I'm less likely to have ballast forward. 25 horsepower motors were typical when my boat was designed; the engineers may have done things differently given the heavier motors we tend to run nowadays.
13sport	posted 01-22-2007 03:44 PM ET (US) What will you do with the side rails? On my 1976 13' sport moving the thwarts 4 inches forward would conflict with attaching the bottom of the side rail into the the wood that is embedded into the hull. Sport
Boatplans	posted 01-22-2007 05:15 PM ET (US) The further aft the weight, the faster the boat. There will also be a greater tendancy to porpoise as weight is shifted aft. It depends on the load. One passenger forward cancels out any problems with planing off or porpoising. Because the fuel tank should be as far aft as possible, the seat cannot be further after than up against the side of the 6 gallon tank. Place the tank on side opposite the pilot. You will still need a tiller extension. With a pedistal and wheel, the location of wooden backup in the hull determines the location of the seats.
Binkie	posted 01-22-2007 05:49 PM ET (US) With the entire interior moved four inches forward, you could build a nice 12"high fold down seat back for the rear seat, and your passenger could ride in the rear seat also,and be more comfortable. With today's heavier outboards I think the boat would ride much better. If you get an under seat fuel tank, you could test the boat, and see if it would be better riding under the front or rear seat. 13 ft. Whalers with their hooked bottom won`t go fast anyhow, so why bother trying to set it up for speed. As far as looking for embedded wood to screw your mahogany clamps and console too. There are other alternatives to this that work just as well. Rich
teleman360	posted 01-22-2007 10:02 PM ET (US) I messured today and the entire interier was moved back 6". I tried moving it forward, but I will have to get a new steering cable to do this. If I come across a good price for a 10' cable I think I will go ahead and move it. As a side, my OB is a Johnson 28 which weighs 115 lbs. much lighter then todays new OB's.
Boatplans	posted 01-23-2007 12:18 AM ET (US) In most cases, Boston Whaler 13 footers should keep the weight and balance established by the builder, the way the boat was set up when delivered from the factory.
Binkie	posted 01-23-2007 07:05 AM ET (US) boatplans The weight of a late `50`s 25hp motor was just slightly over one hundred pounds. I believe modern motors with the additional weight, make is necessary to experiment, with driver and passenger locations. Rich
13sport	posted 01-23-2007 12:06 PM ET (US) How about a genuine certified engineer weighing in on this discussion? I would also like to know what Clark Roberts thinks of moving the stock interior forward. What about those who have converted a 13' to a center console. Did you move the center of gravity forward? I am think of re-powering with a 210lb four stroke. I am looking at all of the options of maintaining the current static trim. Moving the interior forward is a option that I haven't thought about. Sport
Boatplans	posted 01-27-2007 05:28 AM ET (US) Binke, You make a good point. When it comes to a heavy 4 cycle outboard, hydraulic tilt and trim should help. Securing a 12 gallon tank under a seat precludes shifting conventional 6 gallon tanks as needed to trim the boat.
Tom Hemphill	posted 07-22-2007 12:13 PM ET (US) This is to follow up on my expressed interest in moving the interior forward a little. From screw hole evidence, it looks like mine had already been moved forward 2 inches. I was able to go forward an additional 3 inches and still attach the base of the console to embedded wood under the deck. (Thanks, CW, for providing the wood locating drawing.) Yes, I'll have to relocate my side rails forward, but there should be hidden wood there, too. The front of the console is now 63 inches from the inner transom. I believe the distance between the thwarts is as originally built. I have 22 inches behind the aft thwart, possibly enough room to build a small storage compartment and backrest. My 6-gallon gas tank and battery continue to live in the stern. The change in performance is minor, but suits my needs. With one aboard, it gets on plane extremely easily (~ 10 MPH) and goes plenty fast for me (around 30 MPH) when I want, while retaining very stable handling. Power tilt and trim would be nice, but I don't want the added weight, cost and complexity. My 1987 35-HP Mecury weighs around 200 pounds. I think if such a motor had been standard-issue in 1966, the interior would have been located as mine is now. I feel I have a very predictable and safe skiff which handles a variety of tasks competently.
renoduckman	posted 07-22-2007 07:20 PM ET (US) I had a 72 13ft for 13 years. It was a tiller boat. But one thing i do know that it was rear heavy for sure. It had the wood seat move forward and we considered moving it even more. I kept the 6 gallon Merc tanks in front of the seat. Seemed to me it had a better ride with 2 people and gear near the bow. I think id experiment with it for sure. Test first.
Binkie	posted 07-22-2007 07:21 PM ET (US) Tom, I`m happy that moving the interior on your 13 footer worked out for you, and you didn`t find any negatives. Its possible you may have lost a minuscule of performance, but easier planing and minimal to no porpoising will more than make up for it. Does the boat seem wetter, and does the bow ride lower when at speed? My 13 footer is two or three weeks away from a water test. I moved the custom side console interior about five or six inches forward. The console is much larger than original. The rear thwart is raised 4", 2, 6 gallon tanks and the battery sit under the rear thwart, I built a 32lb, 23" wide,teak rear casting platform,behind the rear thwart. The outboard is a `58, 35hp Evinrude Lark which is a lightweight by todays standards. Rich
Tom Hemphill	posted 07-22-2007 09:05 PM ET (US) I would say that yes, the bow is a little lower at speed. I expect that it would be wetter as a result, but my testing thusfar has been on quite flat water. In the ocean I might trim the motor out one notch. (It's now using the middle of five possible trim positions.)