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Took my 15' out yesterday. Running at wide open throttle, I tipped 31 mph (by gps on my finder). With a 50 hp Merc. is this reasonable and appropriate? FYI, I'm a newbie and this is my first boat.
Craig in windy Kansas
Craig - Congratuations on splashing your 15. I'm sure you had a blast.
Can you tell us what year your Mercury is? If it is early to mid 80s or older then the hp was rated at the flywheel (rather than at the prop which is how modern engines are rated). If its an older Mercury 50 rated at the flywheel it is closer to a 40 - 45 hp engine by today's standards and 31mph is in the right ballpark. If it's newer and the hp rated at the prop you should be seeing at least 35mph.
Can you also tell us how high your engine is mounted, what the wot rpm is, and what prop you are running?
Edited by wlagarde on 09/17/15 - 7:45 PM
1976 Sport 15 w/ 2005 50hp Nissan 2 stroke
Thanks. 1978 Merc. Measured it from the gps in mph. Not sure of prop (came with it), the depth or the rpm. Is it important for me to know that? (Remember, I'm a newbie.) Somebody on this forum or CW compared piloting a 15 to driving a sports car...I must agree.
Craig in windy Kansas
Edited by cleep1700 on 09/18/15 - 4:20 AM
1978 Sport 15' with 50 hp Mercury
cleep1700 wrote:
Thanks. 1978 Merc. Measured it from the gps in mph. Not sure of prop (came with it), the depth or the rpm. Is it important for me to know that? (Remember, I'm a newbie.) Somebody on this forum or CW compared piloting a 15 to driving a sports car...I must agree.
Craig in windy Kansas
Yes they are fun to drive indeed.
The basic concept is to raise the engine as high as possible (2 or 3 holes up) while not aerating while rising onto the plane. This will result in the least resistance/drag). Then the goal is to prop the boat so you are running at the upper end of the rpm operating range for your engine when you are running your lightest typical load.
The old Mercury 4 cylinder 50 was a very strong engine, and i have seen other 15's where this engine runs 35 MPH as mentioned above on a 15.
If everything checks out (carbs, electronics, timing, plugs etc), it sounds like your older engine may simply be worn out, or for some mechanical reason, not putting out the power it should be. In this situation, this usually means the engine needs a teardown and rebuilding of the block and reeds.
I would begin by checking compression on all 4 cylinders.
Now all of this assumes the hull is in good shape, not overloaded, not poorly bottom painted or with major hull/bottom repair at some earlier date.
