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Author Topic:   belly tank removed

hando posted 05-29-2003 08:07 PM ET (US)
Hello guys, I'm looking at a 1975 outrage 21. The guy has removed the belly tank and went with saddles. Is that a problem? Does the belly tank have structural value? Thanks in advance.
dfmcintyre posted 05-29-2003 08:29 PM ET (US)
Hando -
I removed my internal tank and ran with two 12 gallon tanks under the reversable pilot seat for a year before installing a new 40 internal. Had first planned on equipping it with two 18 gallon saddle tanks, even to the point of ordering the 18's and having some stainless steel brackets made to hold the ends of the tanks.
Decided on going back with the internal.
No real structural need. If the boat your looking at has a RPS, you can easily have capacity for 60 gallons. Then you cut the tank lid into pieces, and have additional storage, abeit wet though. I drilled and inserted a drain between the tank cavity and the rear bilge.
Don
Jerry Townsend posted 05-29-2003 10:17 PM ET (US)
The internal tank does not provide any significant structural benefit - BUT - it does have significance regarding buoyancy. That is, the tank was considered in the buoyancy calculations - as the internal tank would exclude water. Removing the tank would allow water to occupy that space in the event that you were taking on water. Sixty gallons of water is a lot of weight - well about 510 pounds - which might make the difference between float or sink. ---- Jerry/Idaho
spotsnspecks posted 05-30-2003 11:55 AM ET (US)
How is /was the space from the belly filled. Is it foam filled. If you have access to see "what lies underneath" I would check out the condition of what surrounded the belly. I have the dilemma of replacing a "condemned" belly tank on a 1977 Revenge. I will fish this summer with my saddle tanks and get on the resurrection of the old and construction of the new sometime in the winter.
For an interesting read on a similar problem/solution with great pics and narrative see:
http://continuouswave.com/whaler/cetacea/cetaceaPage70.html
John W posted 05-30-2003 01:56 PM ET (US)
I disagree somewhat with Jerry on the bouyancy issue. Assuming the belly tank is filled with gasoline the space wouldn't be adding any floatation. Gasoline is lighter than water, but not enough to matter in keeping the boat floating. There is certainly plenty of foam floatation in your whaler to not worry about that anyway.
I agree that the tank won't provide any structural benefit. In theory, the side tanks vs the belly tank might raise the boat's center of gravity, but on a stable, flat bottom boat such as yours that won't matter either.
Jerry Townsend posted 05-30-2003 02:21 PM ET (US)
John W - you are right and I realized that situation last night after crawling into bed - there is 2 lb/gal difference in the weight (water: 8.3 lb/gal, gasoline: 6.3 lb/gal). The difference in weight with the 60 gallon tank ONLY removed would be 120 pounds - which is not a lot.
But generally, foam around the tank is removed in the process of getting the tank out. If not much foam is removed, that is not a big problem.
The other thing I should have mentioned is that that the buoyancy calculations used for foam design details would have been based on a full gas tank - or 60 gal. in this case. ----- Jerry/Idaho

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Author	Topic: belly tank removed
hando	posted 05-29-2003 08:07 PM ET (US) Hello guys, I'm looking at a 1975 outrage 21. The guy has removed the belly tank and went with saddles. Is that a problem? Does the belly tank have structural value? Thanks in advance.
dfmcintyre	posted 05-29-2003 08:29 PM ET (US) Hando - I removed my internal tank and ran with two 12 gallon tanks under the reversable pilot seat for a year before installing a new 40 internal. Had first planned on equipping it with two 18 gallon saddle tanks, even to the point of ordering the 18's and having some stainless steel brackets made to hold the ends of the tanks. Decided on going back with the internal. No real structural need. If the boat your looking at has a RPS, you can easily have capacity for 60 gallons. Then you cut the tank lid into pieces, and have additional storage, abeit wet though. I drilled and inserted a drain between the tank cavity and the rear bilge. Don
Jerry Townsend	posted 05-29-2003 10:17 PM ET (US) The internal tank does not provide any significant structural benefit - BUT - it does have significance regarding buoyancy. That is, the tank was considered in the buoyancy calculations - as the internal tank would exclude water. Removing the tank would allow water to occupy that space in the event that you were taking on water. Sixty gallons of water is a lot of weight - well about 510 pounds - which might make the difference between float or sink. ---- Jerry/Idaho
spotsnspecks	posted 05-30-2003 11:55 AM ET (US) How is /was the space from the belly filled. Is it foam filled. If you have access to see "what lies underneath" I would check out the condition of what surrounded the belly. I have the dilemma of replacing a "condemned" belly tank on a 1977 Revenge. I will fish this summer with my saddle tanks and get on the resurrection of the old and construction of the new sometime in the winter. For an interesting read on a similar problem/solution with great pics and narrative see: http://continuouswave.com/whaler/cetacea/cetaceaPage70.html
John W	posted 05-30-2003 01:56 PM ET (US) I disagree somewhat with Jerry on the bouyancy issue. Assuming the belly tank is filled with gasoline the space wouldn't be adding any floatation. Gasoline is lighter than water, but not enough to matter in keeping the boat floating. There is certainly plenty of foam floatation in your whaler to not worry about that anyway. I agree that the tank won't provide any structural benefit. In theory, the side tanks vs the belly tank might raise the boat's center of gravity, but on a stable, flat bottom boat such as yours that won't matter either.
Jerry Townsend	posted 05-30-2003 02:21 PM ET (US) John W - you are right and I realized that situation last night after crawling into bed - there is 2 lb/gal difference in the weight (water: 8.3 lb/gal, gasoline: 6.3 lb/gal). The difference in weight with the 60 gallon tank ONLY removed would be 120 pounds - which is not a lot. But generally, foam around the tank is removed in the process of getting the tank out. If not much foam is removed, that is not a big problem. The other thing I should have mentioned is that that the buoyancy calculations used for foam design details would have been based on a full gas tank - or 60 gal. in this case. ----- Jerry/Idaho