Thread subject: Whaler Central - Boston Whaler Boat Information and Photos :: My whaler 13 is only going 25MPH WOT
Posted by bennythomson on 07/24/15 - 8:29 PM
#1
My whaler only goes around 25 mph with 2 people and 6 gallons of gas at full throttle. The engine does only go up to 5000RPM at WOT, I'm not sure why it doesn't go up to 5500. Maybe I'll have the timing checked.
The trim is manual, and it at the second hole from the top. I'll try tilting it more.
The motor is also on a jackplate, but the cavitation plate is about an inch under the keel.
Do these sound like plausible reasons for the lack of speed? The engine runs well, just doesn't get to 5500
Posted by bennythomson on 07/24/15 - 8:35 PM
#2
Forgot to mention -- engine is a 1980 40HP Mercury 2 Stroke
Posted by butchdavis on 07/25/15 - 6:25 AM
#3
Is your speed based on a GPS reading? WAter speedometers are notoriously inaccurate.
Assuming you have adjusted the trim for best performance the first thing I would do to further improve performance is raise the engine at least high enough that the plate is not below the keel. Then I would check to see if the plate is below water while the boat is on plane. If the plate is below water I would try raising the engine another notch and repeat the process until the plate is running right at water level or very slightly below. This is the least cost first step.
A second step is to ensure your engine is in good tune.
If the engine mounting height, trim angle and tune are correct and the RPM remains low I would seek advice on a propeller change. Folks will need your propeller information, diameter, pitch and anything else you know.
Posted by freeportd on 07/26/15 - 2:10 PM
#4
I see that your boat is a 1967 Whaler 13 - which means the engine should be a short (15") shaft. If your Mercury is a long shaft (20") that would explain the problem.
Posted by bennythomson on 07/26/15 - 3:49 PM
#5
It is a longshaft, but I have it on a jack plate.
Posted by dgoodhue on 07/27/15 - 11:37 AM
#6
From my experience with a jackplate, the the cavitation plate should be atleast 3" above the keel. The motor is just mounted too low. Mount it in the 3 holes up position and raise the jack plate as high it will go or until you get to 3" above the bottom.
Posted by bennythomson on 07/27/15 - 3:58 PM
#7
How would I mount it up? The motor is actually on a TH Marine Mini-Jacker, which is not really what the jackplate was designed for but it was cheap.
Here are pictures:
http://i.imgur.com/XlwaDBH.jpg
http://i.imgur.com/fnJCvvm.jpg
http://i.imgur.com/jaYe8KA.jpg
I know it's really ghetto, but the whole thing cost me $150. Could I safely move the jackplate up even more? Or should I pull everything off and have the transom built up to 20"?
Edited by bennythomson on 07/27/15 - 3:59 PM
Posted by WE Whaler on 07/28/15 - 7:31 AM
#8
It looks like this bracket has multiple holes so it looks like you can raise the bracket (change the holes you are using).
Posted by dgoodhue on 07/29/15 - 10:18 AM
#9
The bracket that he has isn't going to make up the 4" difference. His motor also clamps which limits the mounting height as well. It doesn't look like even has the lower bolts either. I would drill the mount for those holes; my friend lost his 25 hp motor overboard by just using the clamps.
Posted by bennythomson on 07/29/15 - 8:16 PM
#10
Yea I've heard some horror stories about clamp ons. I think I'll build up the transom to 20" this winter and then put the jackplate on.
Posted by Phil T on 07/30/15 - 2:31 PM
#11
I would get a better bracket, try Bob's Machine Shop. What you have is too small with the bolts too close together.
As for the engine clamps, you could replace the clamps with nuts and bolts and a spacer block.