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donzidon
09-01-2017, 10:22 PM
I have our late Harbormaster's old boat. It was modified by Donzi to carry an outboard on the transom, and Scott converted it back to a Bravo outdrive with a raised X dimension. I am running a Revolution 4 prop, and the boat hooks up OK, but it runs very flat at speed and hits pretty hard when you take a wave. With the raised X dimension, my ability to pick the bow up with the motor is pretty limited.

It has an enormous gas tank that comes right up to the floorboards the full length of what I believe is usually a locker down the middle of the cockpit. The work order indicated that it holds 80 gallons. I am wondering if Donzi moved the tank forward to balance the extra weight of the outboard motor hanging off the transom.

There are no 22s around here for comparison, so I am not sure where the fore and aft center of gravity should be on a stock boat. However, the boat definitely rides with the bow lower when the tank is full, and it rides better when I have people sitting in the back seat. Also, it does porpoise quite a bit in the 40s, and the tabs don't seem to be very effective. They tend to make the boat crab as much as push one or the other side of the bow down.

Do you think that the gas tank could be an issue? I would appreciate knowing where the tank is on a stock boat. Reading around the forum, I understand that it runs around 55 gallons, so my fuel load must be around 150 pounds more than stock.

Thanks in advance for your advice,
Don

yeller
09-02-2017, 11:40 AM
Here's a pick of my tank with the deck off. The pedestals are set where they would be with the deck on. The tank is pretty much 100% forward of the seat bases.

All these boats porpoise around 40 and if you don't hit a wave perpendicular, they will hit hard. Even with a raised x though, you should be able to get the bow up without a problem.

I'd suggest trying different props, 3 & 4 blades. No one can tell which prop will work, because every boat is different. Don't expect a cure-all prop, but you might find one that works better for you.

donzidon
09-02-2017, 11:11 PM
It looks like my tank extends all the way back to the bench seat, so I guess the fore/aft balance should not be affected too much. It is a lot of gas to carry, and I do notice that the bow rides lower when the tank is full. The boat seems to ride better with more people on board, particularly in the back seat.

The revolution 4 prop was a great improvement. I could barely get it up on a plane with the 3 blade that I was running before. I do start to get slip pretty quickly when I start trimming up. Based on this experience, I would not recommend the raised X dimension to anyone else.

best regards,
Don

donzidon
09-02-2017, 11:12 PM
PS - I really like those cross braces across the top of the tank. That is going to be a very strong and stiff assembly when done.

Greg Guimond
09-02-2017, 11:19 PM
If you want to get the real C o G the best thing to do is strap it. I'd fill it with gas and then you will know what you have to work with instead of guessing. It's not that hard to do. I believe that boat started with a set of twins btw.

gcarter
09-03-2017, 05:33 PM
The straps were used by Donzi on poly tanks.The preferred
method by most folks of retaining aluminum tanks is 4#
foam. The stock tank is 6'-4" long and looks like this: