Comanche3Six

I slept at a Holiday Inn express last night and my boat will do 74 mph with a full 100 gallons of fuel and 82 with about 10 gallons left. Usually, regular unleaded gasoline has a gravity of around 58 and a weight per gallon of 6.216 pounds per gallon. Premium gasoline may have a gravity of 54, or 6.350 pounds per gallon

Jamie B.

Interesting. You have a much higher top speed in your MTI than you had in either of your Fountains, I assume. Thinking about that, you would think that the total top speed of the boat in question might also have alot to do with it (?) . . . will 200 pounds effect a boat that normally can do a 150 mph top speed the same as it does one that does a 65 mph top speed ?

How much does your MTI weight ?

Jamie B.

lol

I round up to 7 per gallon

Jamie B.

How much does this boat weight ?

formula31

Strangely, my boat is faster with a full tank of fuel, probably has something to do with moving the center of gravity to its optimum point. Then, cold air, 1-2 footers is the best.

Jamie B.

How much does your boat weight dry ?

dreamboater

I have heard in twin engine O/B cats, 200lb can equal as much as 2mph. Some boats are just more weight sensative than others, Cats especially. Dont know if there is an exact formula for this. Our 37 Outerlimits actually has run faster loaded down than empty. I am pretty sure that has something to do with not having the right props, but weight has not slowed the boat down as of yet.

Lady X

I personally think that the more iced down cocktails we have on board the faster the boat seems to go

Beak Boater

I think the heaviest thing you can put in a boat is a GPS, the boat always slows down 3-5 mph when you add one of those!!!!

Hydrocruiser

http://www.go-fast.com/boat_speed_predictions.htm

I used this speed calculator and started with a 8500 lb (let's say 35' step hull) and T-500 HP engines. The calculated speed is 86 mph. For every 200 lbs you add you loose exactly 1 mph. If you go down to a lighter boat of say 4,000 lbs, even with the same power and size you loose 2 mph per 200 lbs added. So you are right, the heavier the boat the less effect additional weight has on speed even though the lighter weight boat obviously has a faster (112 mph in this case) top end. The boat does not have to be bigger it's a function of weight in a planing hull. Just as a side note by adding steps you may see an additional 10-15 mph on the top end and to get this same speed gain by decreasing weight using light weight composites it would take a weight reduction of 1,500 lbs to gain the benefit (10-15 mph) of steps. So a non-stepped 35' boat that weighed in at around 7,000 lbs would go as fast as a stepped hull weighing 8500 lbs. If you could get the weight down to 6,000 lbs a "traditional" non-stepped 35' deep V would go 92. So as I see it steps give higher MPH by a simple hull design change with no additional manufacturing costs whereas reducing weight is expensive.

I went the extra mile out of curiosity to figure this out for the fun of it.
Not an easy one to understand.