Boating How-To’s - How to increase top speed on 21' Seahunt Triton 207.

My Dad just bought a 2007 Seahunt Triton 207 21' with a Yamaha 150 4-Stroke. The boat came with trim tabs and a coat of bottom paint from previous owner. The prop is a Mercury Mirage Plus stainless steel 3-blade 19 pitch prop. With two people on the boat I am only able to reach 4800 RPM's and a top GPS speed of 31 MPH. I have a friend with the same exact boat, model, engine, and name brand prop only his has a 17 pitch and no bottom paint or trim tabs. He is able to reach 42 MPH with two people in it at 5200 RPM's. I thought it was a problem with the 19 Pitch prop so we swapped out props with his 17 Pitch and was able to reach 6000 RPM's but still only managed to get 34 MPH GPS speed. The engine has been serviced by a certified Yamaha mechanic and all fluids and oil changed and maintained to date. I am trying to figure out why my friend's boat is able to reach such higher top end speed and what could be slowing down my dad's boat? Thanks for any input or suggestions.

Engine height? Is the cavitation plate completely submerged at speed, or is the top of it just awash (as it should be)? This article should be of help: http://www.veradoclub.com/smf/index.php?topic=137.0

How is he calculating top speed in his boat. Could be the differnce between a speedometer and a GPS calculated speed.

its dumb but i have seen it happen is your gps set to knots per hour or miles per hour? also check engine height like mentioned about. it plays a huge role.

The GPS is set for MPH as far as the height of the motor I am not sure on that. I will have that checked and see if that may solve the problem. We did measure my friends speed with his GPS as well to obtain an accurate speed reading. Thanks for the input and suggestions.

There is something off in the numbers. I am no expert but you are saying your picked up 1200 RPM by dropping pitch from 19 to 17? at most you should see about 400 RPM increase with that change.

Also did your buddy run with the 19P prop? if so what RPM did he see?

With the 19 pitch prop I can bury the throttle all the way down far as it will go and the max RPMs I can achieve is 4800. When I put the 17 pitch prop on with the throttle all the way down I got up to 6000 RPMs. We did not try the 19 pitch on my buddies boat.

I have a sea hunt triton 210 with the same motor, my motor is second ole from top, if this helps any, something is way off on yours.

Have you trimmed the motor up after you got on Plane?

Thanks will check and see what hole the motor is mounted in. Yes I have trimmed the motor up after achieving plane. I trimmed it until it began cavitating then brought it slightly back down and that was when I was able to reach 31 MPH.

Thanks will check and see what hole the motor is mounted in. Yes I have trimmed the motor up after achieving plane. I trimmed it until it began cavitating then brought it slightly back down and that was when I was able to reach 31 MPH.
You trimmed it up until it began to ventilate. It sounds to me like the 19 pitch prop. is in need of repair, that's too much of an RPM difference for 2 inches of pitch.
Did you compare the water lines on the 2 boats? Is there a chance that yours is considerably heavier..... and possibly holding water?

The bottom paint does not help. Where the tabs all the up? Meaning in full bow up state?

Thanks for the correction in terms (ventilate) for (cavitate). I am new to operating a boat and am not familiar with all of the proper terms. I have been on boats all my adult life but always as a passenger so still getting used to actually operating my dads boat and learning as I go. I have not had the two boats side by side in the water to compare water lines. I have had the drain plug out while on the trailer and pulled boat for several miles to allow all the water to drain after running it. I also turned on the bilge pump and pumped all water out of boat until it did not have anything left to pump out. If it is holding water inside still I am not sure how to tell? The prop does not have any visible damage that I can see to it when I took it off and changed it out with my buddies prop. I have heard that bottom paint can slow a boat down but I was not sure if it would be able to cause that much of a loss of speed when compared to my buddies boat. Thanks again for all of the suggestions and input.

I did put the tabs all the way up both at take off and while running because that seemed to give me the best speed. I trimmed the tabs all the way up and just used the motor trim to maximize the speed.

If it is holding water inside still I am not sure how to tell?

Remove a below water line screrw, such as one on the transducer or trim tabs. See if water comes out. Use a sealant when replacing the screw.