boat speed

[boaterntexas]

My boat is a 1976 17.5' haydrasport fiberglass bass boat, which I belive whiegh in the nieghboor hood of 1000 lbs. , the boat has a 155 hp merc with thunderbolt, the motor is 1976 also I belive and its a inline 6 cly. The boat does not seem to be reaching it potential speed, not sure how fast it moves but I would say around 25 or 30 mph, any idea on how fast this boat should be able to go. Oh yeah the prop is in okay shape few small niks, and a tad out of pitch. any suggestions to increase the speed<br /><br />Thanks,<br /> Thomas

 

[OBJ]

Re: boat speed

Hi boaterntexas.<br /><br />Do ya' got a tach to see if the ol' Merc is turning full RPM's? If not, your engine may not be doing all it's capable of for some mechanical reason. Seems you should be going a little faster. I got a 16' Starcraft Super Sport open bow with a 50hp Johnny and by my self I can get about 32 to 33 mph. My boat weighs in at about 1200lbs. with out engine. The prop is very important. Not only for top end but to make sure your lower unit survives. If it's out of kilter, get it repaired. If you know someone local that has experience, have them look at your rig and check the set up. How high is the engine on the transom and does the trim and tilt work OK. All this can effect top end performance.

 

[Boatist]

Re: boat speed

Boaterntexas<br />1000lb and 155HP should have a speed of 60MPH.

 

[OBJ]

Re: boat speed

Hey boatist,<br /><br />I remember some math that was posted once to figure theroetical speed. Is that what ya' used or am I in the wrong ball park.

 

[JasonB]

Re: boat speed

Just for reference, I have a 16' fiberglass that weighs about 1000lbs and my 85hp Johnson V4 shoves it to 32-36. You should be flying with that I6. Like someone else, I would check yor RPM's witha tach.

 

[Jamar]

Re: boat speed

Ditto, that boat should haul butt. Doubt just having the wrong prop could drop speed 30 mph, but it could help. I would check engine rpms and condition out first, then check the propping.

 

[Jamar]

Re: boat speed

Just for reference......every hydrasport/I6 i ever saw on the water was always passin my boat runnin 50.

 

[blazed4x4]

Re: boat speed

Any problems idling? Gotta make sure your hittin on all 6. How do the plugs look after a wide open throttle run?

 

[Jack Shellac]

Re: boat speed

With the motor at rated WOT RPM and if the boat fully loaded weighed 2000 lbs, you should do about 49 MPH. At 1000 lbs, you should get about 69 MPH. This is using JB's formula.

 

[Hooty]

Re: boat speed

Like mentioned above, you need a tach and some sort of speed indicator. Either a speedometer or GPS.<br /><br />c/6<br /><br />Hooty

 

[boaterntexas]

Re: boat speed

UPDATE okay got the tach work and the speedometer. The tach read about 4500 rpm at 35 mph. Not sure if the speedometer is accurate. ON shore I can get teh motor to tach out @ 6000 rpm. But off shore the best I can get is 35 to 37 mph and 5000 rpm everything is trimmed out riht and sounds great, on and off shore. what should I do?<br /><br />Thanks,<br /> thomas

 

[Boatist]

Re: boat speed

OutboardJim<br />Yes I used a formula I got off the board that works on my boat but I did it wrong as just used the tiny bit of information given. I did not try to figure correct speed as not enough info given. Do not know weight of motor, fuel, gear and passangers as not given, so just used 1000 lb and 155 HP. Kind of a poor effort on my part.