using your formula - that boat would go a lot faster with a 200. That's what I'd get.

 

Ok I'm not understanding how a 200 is gonna make it go faster than 300hp. Or did you mean twins. Honestly the 300hp i was referring to with that formula was with twin 150.

 

Kidding - my ~4000 lb boat (deep V - hard top) with a 250 tops out at about 42 mph

 

Humor

 

Brah, if you divide up 300 by 3 you get 100

If you divide up 300 by 2 you get 1 fiddy.

What he's trying to say is, your formula is not correct.


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What he is asking about is weight per horsepower. With 300HP he is looking at 28 pounds per HP. With 200HP it would be 42 pounds per horsepower.

My boat has a 21 degree V and weighs about 4,000 pounds (20 pounds per HP). I have a 200HP motor and top out at 50 mph light, 46 mph loaded down.

 

My 800 lb deep v hull with a 300 hp motor tops out at 70 mph limited by a coast guard mandated motor governor. Now that the warrantee is over Im wondering what de bugging that governor will produce.

 

... Fun. 😀

 

I have a gradywhite that weighs 4700# with twin 150 yamahas it topped at around 50 mph then I got bottom paint now it does about 47 mph just bottom paint made a difference

 

I had a boat of similar weight with twin 200 four strokes and it pushed 46 MPH trimmed out with 4 adults and gear- hope that helps

 

Boat weighs 2900# from factory. With full equip, 6 crab traps, an suzy 250 and two fat boys 250# each we did 55mph. With another adult and two kids we did 50mph... not too shabby for an old scowl.

 

mid 30's to low 40's,

what do I win lol

 

This is all guesswork at this point but .... 'Surprise' projected loaded weight at 7500# pushed by 300 hp counter-rotating prop set = 25. I'm guessing at least 35 when the fish box high level alarm is blaring, might be a little faster. We will see pretty soon as the go fast gets installed next week.

BTW none of that matters on Big blue. Like the speed of light (ultimate speed limit) .. there is a speed limit imposed by sea state, aluminum boats and sore backs. Ride quality is controlled by the throttle hammer. About 22 kts on reasonable days. Slower on the days you wished you had stayed home.

 

I'll play. Tunatinder is about 10k and is about to get new to me 250's bolted to it. So 10k / 500hp = 20lbs per HP. Previously had 225's, so it would have been 22lbs per HP. With that configuration the economical cruise speed was 25-30mph and topped out at around 44. Hoping the 250's will bump my cruise to 30-35, when the ocean allows. Basic math would tell me I'll only get a 10% gain going from 225's to 250's. However I'm hoping to achieve 15-20% gain due to motor technology differences, fine tuning props/motor mounting, and the hull is designed to be most efficient at around 35mph.

 

10K in weight?

 

A lot of talk about motor size, but what about prop pitch? My friend and I have similar boats and the same HP. He runs a 18.5" pitch and I went with the 17". I easily beat him to 30 mph. My boat tops out at about 35mph he claims to get 40 mph. He can get to the Tuna grounds a little faster on the nice days, but those days don't come that often. I feel safer crossing Bars with the added acceleration and without a doubt get better fuel mileage. The heavier the load the more I like a low pitch propeller.

 

One rule of thumb says a weight to hp ratio of 30 gives you a top speed of 30 mph. Your ratio is 28, which probably gets you a 33 mph top speed. That's just under 29 knots.

I'd say she's a little underpowered, but serviceable.

 

And the fuel burn is....
My boat is 11000 lbs according to the builder. 340hp so 32.5 lbs per hp. The deadrise is called a constant 18 degrees whatever that means.
WOT is 3450 rpm which bumped it to a hair under 35 knots or 40 mph
At 2740 rpm it was 24.7 knots or 28.4 mph...probably can cruise and be easy on the engine at a bit under 3000 rpm but this rpm is more than likely good enough depending on sea condition. I'm not into knocking my teeth out.
My boat has bottom paint which the builder says knocks about a 1 knot off the speed.
The photo was taken bucking into a small 2' chop and an outgoing tide in Grays Harbor. Hopefully the numbers will improve as the engine breaks in some.