how fast should my boat go?

[Bill3434]

Re: how fast should my boat go?

You say the RPM will reach 4700, is this in gear @ 14.3 Knots? We need to get the info squared away first. If you have changed the prop since then, then we need to get the new info. Everything needs to be clear before any conclusions can be drawn.

The conditions need to be the same too. Gear, people, fuel, weather and wind conditions need to be as close as possible too.

 

[QC]

Re: how fast should my boat go?

Yep!! It felt like we were bouncing around in this thread and we need to rewind a little. Personally I find it highly unlikely that she will turn 4700 RPM in gear at 14.3 Knots no matter what is going on. And I don't believe the numbers he gave us for the prop indicate a 26 inch pitch either. The combination above seems impossible unless there is some major issues like ventilation, or bad coupler. With those we would be hearing about smoke and smells and noises etc.

 

[humboldtbrad]

Re: how fast should my boat go?

You say the RPM will reach 4700, is this in gear @ 14.3 Knots? We need to get the info squared away first. If you have changed the prop since then, then we need to get the new info. Everything needs to be clear before any conclusions can be drawn.

yes in gear wot.
I changed the prop as a quantifier if it kicks butt with this prop then likely it is prop slip.

 

[QC]

Re: how fast should my boat go?

That kind of slip is CRAZY. Sounds like she is ventilating to me or the tach is wrong. What does the bottom look like? Did it sound like 4700 RPM?

 

[humboldtbrad]

Re: how fast should my boat go?

That kind of slip is CRAZY. Sounds like she is ventilating to me or the tach is wrong. What does the bottom look like? Did it sound like 4700 RPM?

it is possible the tach is wrong that is always a possibility. but it did sound like 4700. what do you mean ventilating? it is a vee all the way back. is that what your asking?

 

[QC]

Re: how fast should my boat go?

Hull condition we are asking about growth, damage, warping (hook or rocker) etc. Ventilation is when the prop grabs air off the hull and starts to spin up wildly. Usually they will rev up very quickly though. Do you have trim tabs? Do you know how to use them? Are you trimming down to get going? And then trimming out to go faster? All of these seem like possibilities, but I am VERY suspect of the 4700 RPM at that speed.

 

[humboldtbrad]

Re: how fast should my boat go?

it has trim tabs but the pump needs work so no go there.
the hull is in great shape nothing like what your asking.

 

[QC]

Re: how fast should my boat go?

No information from the previous owner available?

 

[humboldtbrad]

Re: how fast should my boat go?

nope not regarding to speed.
although the engine was rebuilt and has about 80 hours on it and supposedly the drive was went through at the same time but i dont have paperwork to back that up.

 

[UncleWillie]

Re: how fast should my boat go?

Something just doesn't add up.
4600 rpm at 14 knots is crazy.
A 25 Ft Boat with 265hp should at least get on plane.

The trailer is still attached, The trim is Full Up, Or he is dragging a body!
An 11 x 26 prop would be something used on a Drag Race Boat.

The Trim is DOWN, Correct?
Is the Stern digging in and are you plowing a huge wake when this happens?

 

[QC]

Re: how fast should my boat go?

For clarity, I bet at 14 knots she is on plane, and even a fairly clean one. That's 16.5 MPH. With that said, not adding up for me either.

 

[haulnazz15]

Re: how fast should my boat go?

Well, I know he mentioned it's a Stringer (OMC) drive, so I don't know if there's anything stringer-specific that would cause it. 265HP ought to be able to push a heavy 24-25' boat 30-35mph at a minimum I'd think, so about twice as fast as what he is currently getting. I hope maybe he misread the prop size (and diameter), 'cause an 11"x26 prop is absurd on this engine/drive/boat.

 

[QC]

Re: how fast should my boat go?

Remember though it is really only equivalent to a 230 hp today.

 

[haulnazz15]

Re: how fast should my boat go?

Remember though it is really only equivalent to a 230 hp today.

Understood, but 230HP will take a 70's 20-21' runabout to almost 50mph. I would imagine adding 4' and 700lbs or so would still get the boat above 30mph on that same power. Obviously kind of apples and oranges, but it doesn't seem like an unreasonable expectation. If he's got waterlogged foam and/or stringers, it changes things a bunch.

 

[UncleWillie]

Re: how fast should my boat go?

If he is on plane at 16mph; that is still strange.
I can slow down to 16 and still maintain plane.
But if I keep adding power to get onto plane, as soon as I hit about 13-14 and come up on plane,
All the extra power need to get over the top suddenly speeds me up into the mid 20's

Getting just barely up to 16 and still plowing feels more reasonable.

 

[QC]

Re: how fast should my boat go?

Getting just barely up to 16 and still plowing feels more reasonable.

Agree that.

 

[Howard Sterndrive]

Re: how fast should my boat go?

230HP will take a 70's 20-21' runabout to almost 50mph.

His 25 footer could weigh as much as two 20 footers. I bet it has never gone over 35 mph. I would be expect around 30mph at wot.

If any of the data is accurate, I suspect the engine is way low on power and someone has compensated by changing props or drive ratios. That's the only was 17mph on plane at 4600 rpm is going to be possible for any length of time.

 

[humboldtbrad]

Re: how fast should my boat go?

I'm estimating the boat weighs in the 7000 pounds range and the data is as accurate as I can give im not sure what the problem is the engine is in awesome condition I highly doubt it is a problem with the engine.
how would I check/find out what the gear ratio of the drive is? what should it be?
I'm likely going salmon fishing in it this weekend so with the different prop I will get more data.

 

[BonairII]

Re: how fast should my boat go?

Has compression been checked on the motor?

 

[drrpm]

Re: how fast should my boat go?

The gear ratio is stamped on my alpha outdrive. In general if a story doesn't make sense there is something missing.