Another boat speed question

[java230]

Just wondering if what I'm getting is about what i should expect as far as speed goes.

Boat:
1983 Coho 134, a 13' whaler clone.
Motor 1982 Mercury 2 stroke 40 HP. Ill have to check the prop size and pitch tonight.

Package should be 7-800 lbs. Maybe a bit more. I may try to weigh it.....

My Wife, 4yo Daughter and I, and our gear, id estimate it about 600lbs total.

Planes and does about 20 MPH WOT, via GPS. I hit 21.2 with the wind and calmer water. It

Does this sound about right for this set up? Im coming from a little tinny so not quite sure what to expect.


since everyone likes pics. this was last weekend.

 

[java230]

Re: Another boat speed question

Pulled the prop, its a Michigan 3 blade, 10.25 inch, 14 pitch.

 

[Another retired guy]

Re: Another boat speed question

Some more info may help you get an answer. Do you have a tach? Without knowing the rpm at WOT it's impossible to say if you're getting the most out of the motor. Does it rev easily to max from a standing start and get on plane quickly, or not?

 

[java230]

Re: Another boat speed question

Some more info may help you get an answer. Do you have a tach? Without knowing the rpm at WOT it's impossible to say if you're getting the most out of the motor. Does it rev easily to max from a standing start and get on plane quickly, or not?

No tach unfortunatly, id love to add one at some point.

It revs right up, but isnt fast to plane. It does have dolphin fins on the AC plate. The motor does sound like its running happily at WOT. But hard to tell RPMs from 2 stroke noise...

No powered tilt or trim, Trim pin is in the 3rd hole, it feels pretty level on plane.

 

[Another retired guy]

Re: Another boat speed question

No tach unfortunatly, id love to add one at some point.

It revs right up, but isnt fast to plane. It does have dolphin fins on the AC plate. The motor does sound like its running happily at WOT. But hard to tell RPMs from 2 stroke noise...

No powered tilt or trim, Trim pin is in the 3rd hole, it feels pretty level on plane.

The fin will help get you on plane, but "may" be taking a bit off the top speed. Have you tried moving the motor one hole out? The boat shouldn't be running too level, bow should be up a little.

 

[java230]

Re: Another boat speed question

The fin will help get you on plane, but "may" be taking a bit off the top speed. Have you tried moving the motor one hole out? The boat shouldn't be running too level, bow should be up a little.

Ill try it this weekend! The fins were on it when i bought it, just a couple weeks ago, so im still learning the boat.

 

[Another retired guy]

Re: Another boat speed question

Ill try it this weekend! The fins were on it when i bought it, just a couple weeks ago, so im still learning the boat.

Changing the trim and/or redistributing weight can make a noticeable difference on speed. This article may help

Trim Your Boat

 

[java230]

Re: Another boat speed question

Trimmed up one hole, gained about 1mph even with the ladies laying on the bow. Before I was doing about 18.5 with them up there. Today was 20-21 with them up there and constant 21 ish with them centered.

To get onto plane was about 10 seconds, and I could plane at about 15 mph slowest. With the doel fins.

 

[jestor68]

Re: Another boat speed question

This subject is also ongoing in the prop section.

We'll see what the new tiny tach says; but I estimate that right now you are running around 4K rpm at WOT.

That means that you'll need to get a 10/11 pitch prop; but we'll have to wait and see what a tachometer says.

The Doel Fin should not cause any speed lose at the speeds your boat is capable of ( it's good to about 40 mph before drags starts to affect it).

 

[java230]

Re: Another boat speed question

This subject is also ongoing in the prop section.

We'll see what the new tiny tach says; but I estimate that right now you are running around 4K rpm at WOT.

That means that you'll need to get a 10/11 pitch prop; but we'll have to wait and see what a tachometer says.

The Doel Fin should not cause any speed lose at the speeds your boat is capable of ( it's good to about 40 mph before drags starts to affect it).

Yes it is in the prop section also, I was hoping to get more input. We will see what the tach says! I think I'll leave the fins for the time being.