Old (lurker), New member with questions!

[ho1ywars]

Whats up guys? Long story short I have been eying up a SC for two year now and finally pulled the trigger this January on a 15' jet. $300 got me a red and white (yellow white) boat gutted, a 25hp motor torn down, and a trailer just redone. So I repainted the white, put a new teleflex system in it, new optima battery, new name, a 1970 merc 402 (2cyl 40HP), and a bunch of small stuff.

I have two main questions.

1. Im only getting 26mph on GPS. The motor is turning @ 5100 RPM. I have it trimmed up as much as i can without the front end bouncing up and down. At this time level I get the highest RPM and the highest MPH. I have read the WOT is suppose to be 4800 to 5800. Question is why is it so slow? The boat is super light, doesnt even have a floor. I was expecting 33 - 35 MPH. I don't see any numbers on the outside of the prop... is the number on the inside of the hub?

2. Im getting the really funky splash when moving. The boat has a 15" transom, I'm running a 20" motor. Is this why? Attached is some pictures of how low the motor sits to the bottom of the boat, and also a video of the splash I'm talking about. Its almost like its dragging (maybe this is creating enough drag to slow me down a few MPH)


Thanks for the help in advance!


Shawn

VIDEO:

https://www.youtube.com/watch?v=hJjO-6rMsHA&list=UU25de-nVwhP6vZZpgtpNVWw

 

[ho1ywars]

Actual boat...

 

[Watermann]

Yeah that 25HP sounds like it's wound tight to me at around 5500 RPMs, your tach may be off. I don't think you'll ever get 35 MPH out of a 25 horse on a 15' Jet no matter what you do.

It looks to me like the stern is heavy, maybe causing the AV plate to go under and kick up that spray. Is the AV plate even with the bottom of the hull when you have the motor tilted down or is it hanging below?

Also your pics are not showing on this end, try using photo bucket please.

 

[MNhunter1]

Long shaft motor on a short shaft transom would be the first place to focus your efforts. Either raise the transom or convert to or find a new short shaft motor.

 

[dozerII]

MN's got it right, there is way to much leg in the water, causing excess drag and not letting the motor run efficiently.

 

[classiccat]

congrats & welcome! :welcome: That boat is moving pretty good! :thumb:

If you love that motor, you'll need a jack plate. A good height to start with is setting the cav plate to be lined-up with the bottom of the hull. The jack plate will provide some setback...this usually affords you the opportunity to raise it a tad more.

 

[ho1ywars]

 

[ho1ywars]

Is this image working for you guys? The cav plate is the one right about the prop right? Ill raise the motor up and give her a shot. Thanks guys!

 

[Watermann]

No the pic isn't showing on this end.

 

[jbcurt00]

There's a link to a youTube video & a single shot of your boat sprouting legs. Else no pix.

From the little of the lower you can see in the 1 pix, it does look too low, by quite a bit. Not sure anything other then a jack plate will lift it the 4-5"+ you need to lift it.

 

[Watermann]

Yeah I see you got the PB account for your pics and are holding out on us!



and I see it's a 40 HP Merc, yeah that should get you going!