how fast should my boat go?

[humboldtbrad]

I have a 1971 25' reinell cabin cruiser the model is rv2450 with a 265hp(i think) chevy 350 and a stringer sterndrive.
I've taken the boat out twice. On my last trip I tried to see how fast she would go and all I could get out of it was 14.3 knots.
question one how do i find out the gear ratio of my drive?
question 2 how do i find out the pitch of my prop?
question 3 how fast should my boat go?

according to the tach my engine will rev to about 4700-4900 rpm if memory serves so I'm pretty sure the engine is in tune

 

[haulnazz15]

Re: how fast should my boat go?

Well, first off, how are you measuring speed? Seat of the pants, pitot-speedometer in dash, GPS? I would imagine that the boat should do around low-40's (mph) or so when propped correctly, but it's hard to say.

 

[humboldtbrad]

Re: how fast should my boat go?

I'm measuring using a gps unit and I confirmed it with my fishfinder that has a speed sensor
will more info help? if so what?

 

[airdvr1227]

Re: how fast should my boat go?

Are you getting to WOT?

 

[humboldtbrad]

Re: how fast should my boat go?

Are you getting to WOT?

yes pedal to the metal, hammer down and so on...

 

[TyeeMan]

Re: how fast should my boat go?

I would say that there is no given speed that your boat SHOULD go. Incidentally, when you're asked are you getting wide open throttle, it doesn't mean do you have the hammer down all the way etc. Rather, WOT means when you have the hammer down all the way is your engine achieving it's maximum rated RPM. It's usually about a 400 RPM swing something like 4200 - 4600 RPM.
That being said, if your engine is running at it's max RPM, say 4600, , your boat speed is what it is at that RPM, you will not be able to go faster unless you start cutting off pieces of your boat to lighten it up, then you can go to the next pich up in prop size.
On the flip side, if you're at full throttle and your engine is going past it's maximum recommended RPM (over revving which is not good) you can then probably bump up one pich in prop size and gain a little speed. That's about it.

 

[GA_Boater]

Re: how fast should my boat go?

When the pedal is to the metal and the hammer is down, what is the WOT RPM? Advancing the throttle fully is WOT, but knowing the RPM at WOT is important to know also.

 

[UncleWillie]

Re: how fast should my boat go?

yes pedal to the metal, hammer down and so on...

No!
Are you getting to 4600-5000 rpm?
Or, is it going above 5000?
Be accurate with this!


The prop info will be somewhere On, or Inside of the prop.
If might look something like this "J14X23P"

 

[humboldtbrad]

Re: how fast should my boat go?

it never went over 5000
it is closer to the 4600 rpm side without a doubt as for exact i cant say
in my opinion it is not over revving. the engine runs great so I'm not really worried about that.
it just seems really slow, really really slow:blue:
truthfully i was expecting about 40mph

 

[airdvr1227]

Re: how fast should my boat go?

If that's true then I believe there is something wrong. It might be waterlogged and weighing much more than it should.

 

[humboldtbrad]

Re: how fast should my boat go?

there is some water in the foam area but not much definitely not enough to cause this

Im starting to think prop slippage. is that a good possibility?

 

[UncleWillie]

Re: how fast should my boat go?

If you were making 4600 rpm the next place to look is a spun hub.
The propeller is not a solid casting.
The center that mounts on the prop shaft is connected to the outer portion on the propeller usually by A big Rubber hub adapter.
If the adapter is slipping (Spun) the engine will run at full speed but the blades of the prop will not.
Kind of like the clutch slipping in the truck.

Place a mark on the innermost part of the prop assembly next to the prop nut,
And another matching mark out by the blades.

Run it at WOT again and see if the two marks still line up.
If Not, The Prop hub is spun.

Or just pull the Prop and Disassemble it and inspect the parts.
If something is wrong it will look really wrong.

It might be as old as the boat, It's Rubber, It's Replaceable.

 

[H20Rat]

Re: how fast should my boat go?

stupid question, but you detached the trailer, right?

 

[humboldtbrad]

Re: how fast should my boat go?

stupid question, but you detached the trailer, right?

wait wait wait..... the trailer comes off? what kind of evil magic is this....

 

[humboldtbrad]

Re: how fast should my boat go?

i changed the prop the one i took off had numbers like 11-26 i think. the one i put on is steeper but didn't have any numbers. so now we can see if it was the prop hub. also where can i get a rebuild kit for my prop?

 

[ktbarrentine]

Re: how fast should my boat go?

Interesting info here:

An introduction to propeller repair

 

[haulnazz15]

Re: how fast should my boat go?

If that is a 3-blade prop, it sounds awfully high in pitch, and would be the reason for your high RPMS and possibly the speed, too. It's also really small in diameter if it's only 11". I believe most props on MC-1/Alpha I drives run between 14-15 1/2" and 15-21 on the pitch depending on gear ratio in your outdrive.

 

[ondarvr]

Re: how fast should my boat go?

I don't think you will get anywhere close to 40 MPH with this combo, maybe the mid 20's or so, it's a big heavy boat.

I also don't think the hub is spun on the prop, if it slips that much the rubber will typically fail completely rather quickly, and the RPM's will increase rapidly well past the 4,700 +- RPM range you indicated.

 

[Bill3434]

Re: how fast should my boat go?

there is some water in the foam area but not much definitely not enough to cause this

Im starting to think prop slippage. is that a good possibility?

You'd be suprised how water logged effects a boat. Any water soaked foam is to much. IMHO

 

[QC]

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.