Top Speed -Does this sound correct

[SNye45]

Hi all,

Last year I purchased a 20ft Aluminum ThunderJet with a Suzuki 115 hp. Because I live at 3,000 ft the dealer switched the prop from a 21'' pitch to a 19'' pitch.

Having done the run-in for the engine, I recently "tested" the top speed at WOT. This turned out to be 5,800 rpm and 36 mph. (The wife, myself and the dog aboard)

Question. Does this sound "reasonable" or am I "under proped"? Suzuki states the rev range is 5500 to 6,000.

I would appreciate any comments. Thank you

 

[frozenokie]

Re: Top Speed -Does this sound correct

Hmmm.... "ThunderJet"... Is that a jet lower unit on your outboard? If so, I know from experience in running the rivers in Alaska with my 24 ft. river boat. I used a 60HP Merc w/ a jet drive lower unit. It would max about 25-30 MPH heavy to light. It was also more of a jon boat style and very light anyway. When using a jet lower unit, you lose a little top end just for the fact that it is a jet drive. The RPM's sound just right or a little high, but a 115HP pushing a 20 ft. boat... Is it a bass boat or river boat? Usually, a 150HP to 200HP engine is mounted to a bass boat that long anymore. And with it you get the higher and speeds. I'm thinking it's about right if you ARE using a jet drive style lower unit.

 

[steelespike]

Re: Top Speed -Does this sound correct

Based on the rpm range I'm guessing you have a 4 stroke and they like to run the 4 strokes close or at their max rpm.It appears to me that you are right on if your test weight is your typical load.A 21 would probably put you below the rpm range at about 5,400.Would also hurt your holeshot.

 

[SNye45]

Re: Top Speed -Does this sound correct

Thank you for the comments..

An Update!!
Although the boat is made by ThunderJet, I have a Suzuki 4 stroke 115 hp outboard attached to it (they come with both Jets & Outboards)