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Author Topic:   15-Footer: Locating Fuel Tank

mdono posted 07-14-2015 07:19 AM ET (US)
[The author tells us that he is] closing in on completion of a re-fit [of a Boston Whaler 15-foot hull] with new [SUPER SPORT-style] interior--the type with the storage box behind the rear bench seat--a Mercury 90-HP two-cycle engine, an Atlas Micro-Jacker jack plate with 4-inch setback, and SeaStar hydraulic steering. [The author tells us that he has] decided to go with custom aluminum 12-gallon fuel tank.
[Should the fuel tank be] placed under front bench seat or rear bench seat?
Too much weight in rear is a concern. The battery is back there. and the motor is kinda large. Due to weight aft, [the author is] expecting [the boat's transom] to be pooped under certain conditions and [the author] doesn't want to exacerbate the situation.
Would the weight of a full load of fuel forward of the helm have a negative effect on handling?
Anybody have experience with this?
You collective input will be appreciated.
jimh posted 07-18-2015 07:09 AM ET (US)
[Separated from an older discussion which was revived in order to append this article.]
jimh posted 07-18-2015 07:15 AM ET (US)
If I understand your proposal for the fuel tank, it will just be sitting on the deck. I suggest you can experiment with the fuel tank in different positions on the deck before you fashion some sort of more permanent mounting for it.
I don't think you can find too many Boston Whaler 15-foot hulls with a 90-HP outboard on a set back for direct comparison. Small boats, particularly light, rounded-bottom boats like a Boston Whaler 15-foot hull, will be very sensitive to weight distribution. When I had a Boston Whaler SPORT 15, I used the weight of the fuel tank to help offset my weight sitting at the helm on the starboard side of centerline. I would move the fuel tank to help level the athwartship trim on the boat.
contender posted 07-19-2015 09:56 PM ET (US)
[Build a custom aluminum fuel tank to fit under the front seat.]
jimh posted 07-20-2015 08:38 AM ET (US)
The weight of 12-gallons of gasoline is about 88-lbs. The weight of one adult will be greater than 88-lbs. I do not think anyone would caution that one must never allow an adult to sit on the seat forward of the helm. It seems reasonable that one would not worry about the weight of 12-gallons of gasoline to be located under the forward seat.
dgoodhue posted 07-20-2015 02:17 PM ET (US)
I have 15' with 5" set back jack plate and 260# 70hp motor, 12 gallon tank in the rear.. When I have 2 people in the boat is faster with two people on the rear seat vs one on each seat. I ended using more trim on the motor to offset the person on the front seat.
Russ 13 posted 07-26-2015 01:47 AM ET (US)
I have a 15' set up with a center console & 90 Yamaha.
The custom fuel tank is mounted on the deck inside the console. ZERO problems & no stern squat. Although the Yamaha 90 is lighter than the Mercury 90.
..
I also built a 15' with a 20 gallon custom tank under the seat, battery in the console. This set up also performed well. The 15' Classic works well with weight forward on centerline.
..
The above combinations also eliminated porpoising, common to small Whalers with too much stern weight.
porthole2 posted 08-11-2015 10:42 AM ET (US)
With my 1983 15 I moved the battery to the console and had a custom aluminum tank made and mounted under the seat. Dimensional capacity of the tank was 28 gallons. I usually kept 25 gallons in it. The original tank was about 12 gallons IIRC and also mounted under the seat.
At the same time I replaced the original (as purchased) Mercury 70HP 2 stroke with a Honda 50HP 4 stroke.
Here is a before and after picture for waterline comparison (no change).
http://s96.photobucket.com/user/porthole2/media/Boats/ Whaler%20Sport%2015%20CC%201983/Whaler_03_zpss6n1x1bi.jpg.html?sort=9& o=2
The boat rode well before and after the changes.

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Author	Topic: 15-Footer: Locating Fuel Tank
mdono	posted 07-14-2015 07:19 AM ET (US) [The author tells us that he is] closing in on completion of a re-fit [of a Boston Whaler 15-foot hull] with new [SUPER SPORT-style] interior--the type with the storage box behind the rear bench seat--a Mercury 90-HP two-cycle engine, an Atlas Micro-Jacker jack plate with 4-inch setback, and SeaStar hydraulic steering. [The author tells us that he has] decided to go with custom aluminum 12-gallon fuel tank. [Should the fuel tank be] placed under front bench seat or rear bench seat? Too much weight in rear is a concern. The battery is back there. and the motor is kinda large. Due to weight aft, [the author is] expecting [the boat's transom] to be pooped under certain conditions and [the author] doesn't want to exacerbate the situation. Would the weight of a full load of fuel forward of the helm have a negative effect on handling? Anybody have experience with this? You collective input will be appreciated.
jimh	posted 07-18-2015 07:09 AM ET (US) [Separated from an older discussion which was revived in order to append this article.]
jimh	posted 07-18-2015 07:15 AM ET (US) If I understand your proposal for the fuel tank, it will just be sitting on the deck. I suggest you can experiment with the fuel tank in different positions on the deck before you fashion some sort of more permanent mounting for it. I don't think you can find too many Boston Whaler 15-foot hulls with a 90-HP outboard on a set back for direct comparison. Small boats, particularly light, rounded-bottom boats like a Boston Whaler 15-foot hull, will be very sensitive to weight distribution. When I had a Boston Whaler SPORT 15, I used the weight of the fuel tank to help offset my weight sitting at the helm on the starboard side of centerline. I would move the fuel tank to help level the athwartship trim on the boat.
contender	posted 07-19-2015 09:56 PM ET (US) [Build a custom aluminum fuel tank to fit under the front seat.]
jimh	posted 07-20-2015 08:38 AM ET (US) The weight of 12-gallons of gasoline is about 88-lbs. The weight of one adult will be greater than 88-lbs. I do not think anyone would caution that one must never allow an adult to sit on the seat forward of the helm. It seems reasonable that one would not worry about the weight of 12-gallons of gasoline to be located under the forward seat.
dgoodhue	posted 07-20-2015 02:17 PM ET (US) I have 15' with 5" set back jack plate and 260# 70hp motor, 12 gallon tank in the rear.. When I have 2 people in the boat is faster with two people on the rear seat vs one on each seat. I ended using more trim on the motor to offset the person on the front seat.
Russ 13	posted 07-26-2015 01:47 AM ET (US) I have a 15' set up with a center console & 90 Yamaha. The custom fuel tank is mounted on the deck inside the console. ZERO problems & no stern squat. Although the Yamaha 90 is lighter than the Mercury 90. .. I also built a 15' with a 20 gallon custom tank under the seat, battery in the console. This set up also performed well. The 15' Classic works well with weight forward on centerline. .. The above combinations also eliminated porpoising, common to small Whalers with too much stern weight.
porthole2	posted 08-11-2015 10:42 AM ET (US) With my 1983 15 I moved the battery to the console and had a custom aluminum tank made and mounted under the seat. Dimensional capacity of the tank was 28 gallons. I usually kept 25 gallons in it. The original tank was about 12 gallons IIRC and also mounted under the seat. At the same time I replaced the original (as purchased) Mercury 70HP 2 stroke with a Honda 50HP 4 stroke. Here is a before and after picture for waterline comparison (no change). http://s96.photobucket.com/user/porthole2/media/Boats/ Whaler%20Sport%2015%20CC%201983/Whaler_03_zpss6n1x1bi.jpg.html?sort=9& o=2 The boat rode well before and after the changes.