Does anyone have a Monterey 250cr running a Yanmar 240 diesel ?

SampoSam

Member
Joined
26 Sep 2023
Messages
54
Visit site
Its a 24''pitch four blade prop mercury Marine Bravo 1 - by the way whats the calculation to get to 50 knots out of interest ?
it may not be 1.5 ratio no way of knowing ?
Following numbers stamped on hub 48 831912 24P
 

ChromeDome

Well-known member
Joined
25 Sep 2020
Messages
3,543
Location
Commonly in Denmark. Dizzy Too, most of the time.
Visit site
Its a 24''pitch four blade prop mercury Marine Bravo 1 - by the way whats the calculation to get to 50 knots out of interest ?
it may not be 1.5 ratio no way of knowing ?
Following numbers stamped on hub 48 831912 24P
That prop # seems to be a stainless 4-blade Bravo XS, 24" by the number stated separately at the end. RH (right hand turning is standard).
To my knowledge a great prop with a good grip.

Calculation is:
Every turn of the prop drives it 24" forward. Multiply by shaft rpm and divide to get knots. Excel lingo is =(pitch*(shaft rpm*inch/1000)*60)/1,852).

Your gear ratio should be stated on the sterndrive. If not you could use a laser tacho to show the engine idle speed and at the same rpm measure the prop rpm. Then divide to get the xx : yy ratio (=how many times (1.65?) the engine rpm is reduced in the sterndrive gearbox to result in the read prop shaft rpm).

Maybe a post on the Cruiser forum mentioned could get the answer from someone who knows?
 

ChromeDome

Well-known member
Joined
25 Sep 2020
Messages
3,543
Location
Commonly in Denmark. Dizzy Too, most of the time.
Visit site
Maybe its a 1:65 ratio ?
Yes, maybe.

Then 3800 rpm would give you 45 knots - still way more than expected.

In any case, a true rpm reading would be nice.

With a laser tacho you stick a little reflective tape to a rotating item (flywheel, prop shaft or something), point the laser beam at it and get the reading in digits. Easy!

Ex:
1706986763293.png
 

QBhoy

Well-known member
Joined
11 Mar 2016
Messages
2,612
Visit site
Thanks for your reply. Can i ask what it was like getting up on the plane and what the top end speed was ?. Did you fin the boat heavy and more weight toto aft ?- do you know if the outdrive was a Bravo 1 and would you know prop size ?
Hi there. It was a bravo one. Sounds like the identical boat. This one had a kind of blue finish to the hull sides.
So what I found she was like, was almost quite typical of these sort of boats. Especially a turbo diesel one.

If she had anything more than half a tank of fuel, water in the domestic tank too…never mind some crew sitting at the rear…she was typically North American boat that size, stern heavy.
Made a little more prominent when trying to plane,
Thanks for your reply. Can i ask what it was like getting up on the plane and what the top end speed was ?. Did you fin the boat heavy and more weight toto aft ?- do you know if the outdrive was a Bravo 1 and would you know prop size ?
Hi
Thanks for your reply. Can i ask what it was like getting up on the plane and what the top end speed was ?. Did you fin the boat heavy and more weight toto aft ?- do you know if the outdrive was a Bravo 1 and would you know prop size ?
Hi again...
Yeah, no probs.
She behaved very typical of a North American boat this size, but perhaps a little more emphasised by the turbo diesel engine.
To explain, she and others like her can be very stern heavy...
The boat I knew, if she had a full tank of fuel and water, then the heavy engine of course and throw in a crew member or two the rear seats, you will be then talking about the best part of getting on for nearly a ton or close...right at the very aft end on the boat. Given the length of the boat, things get very stern heavy in such a scenario.
All this considered, the boat now has a very hard task of it, in order to get her planing.
Then it should be considered that she has a Turbo Diesel power plant. Although it is true that your engine certainly has a fair power and HP rating...that rating is made at a certain rpm and when the turbo is producing full boost and on song.
That in mind, that turbo needs to get on boost first off to produce the power in the first place. So as a result when trying to get planing initially, there is a very obvious lag and dead spot until she manages to spool up the turbo. That said, once she does get on boost, she performed well and managed into the early 30's from memory.
So best we found to get her going, was to only have the fuel in the tank required, plus a margin on top for safety obviously. We also used the trim tabs to help her along too.
Hope that helps a little at least. Lovely boat I thought. Only slight critique from me might be that she may have been a little tippy when on the plane in a cross wind or if little thought was given to clever passenger weight distribution when underway. Typical behaviour of a narrow deep v hull like that perhaps. Especially if she was to have her canopy up and catching the wind perhaps

Hope that might help you a little at least. If you like, I might be able to find out what prop size she maybe had on her. I am almost sure she had either a bravo diesel specific outdrive or a bravo 3 type diesel specific outdrive perhaps. Can't quite remember now. The boat has since been sold on, but the owner at the time might just remember some further details if I was to ask him.

So to quickly answer your main question..yes, use the tabs initially to assist the planing. This helps hugely. But be quick to lift them back up as you do get planing, or she may take am unruly wobble to one side. Never a nice thing when it happens, I found.
 

SampoSam

Member
Joined
26 Sep 2023
Messages
54
Visit site
Hi there. It was a bravo one. Sounds like the identical boat. This one had a kind of blue finish to the hull sides.
So what I found she was like, was almost quite typical of these sort of boats. Especially a turbo diesel one.

If she had anything more than half a tank of fuel, water in the domestic tank too…never mind some crew sitting at the rear…she was typically North American boat that size, stern heavy.
Made a little more prominent when trying to plane,

Hi

Hi again...
Yeah, no probs.
She behaved very typical of a North American boat this size, but perhaps a little more emphasised by the turbo diesel engine.
To explain, she and others like her can be very stern heavy...
The boat I knew, if she had a full tank of fuel and water, then the heavy engine of course and throw in a crew member or two the rear seats, you will be then talking about the best part of getting on for nearly a ton or close...right at the very aft end on the boat. Given the length of the boat, things get very stern heavy in such a scenario.
All this considered, the boat now has a very hard task of it, in order to get her planing.
Then it should be considered that she has a Turbo Diesel power plant. Although it is true that your engine certainly has a fair power and HP rating...that rating is made at a certain rpm and when the turbo is producing full boost and on song.
That in mind, that turbo needs to get on boost first off to produce the power in the first place. So as a result when trying to get planing initially, there is a very obvious lag and dead spot until she manages to spool up the turbo. That said, once she does get on boost, she performed well and managed into the early 30's from memory.
So best we found to get her going, was to only have the fuel in the tank required, plus a margin on top for safety obviously. We also used the trim tabs to help her along too.
Hope that helps a little at least. Lovely boat I thought. Only slight critique from me might be that she may have been a little tippy when on the plane in a cross wind or if little thought was given to clever passenger weight distribution when underway. Typical behaviour of a narrow deep v hull like that perhaps. Especially if she was to have her canopy up and catching the wind perhaps

Hope that might help you a little at least. If you like, I might be able to find out what prop size she maybe had on her. I am almost sure she had either a bravo diesel specific outdrive or a bravo 3 type diesel specific outdrive perhaps. Can't quite remember now. The boat has since been sold on, but the owner at the time might just remember some further details if I was to ask him.

So to quickly answer your main question..yes, use the tabs initially to assist the planing. This helps hugely. But be quick to lift them back up as you do get planing, or she may take am unruly wobble to one side. Never a nice thing when it happens, I found.
Many thanks that's very helpful. They certainly do seem to be stern heavy boats. I was running a full tank of fresh water ( not sure why ?) which i have now emptied plus i have loads of heavy tools which i will also take off. I am told that you shouldn't need to use trim tabs but it seem logical to help get up on the plane. Also feel weight distribution is important and needs some ballast on bow as so stern heavy. Would appreciate if you could find the prop size as everyone i have spoken to has a different opinion !
Thanks again fir your time
 

ChromeDome

Well-known member
Joined
25 Sep 2020
Messages
3,543
Location
Commonly in Denmark. Dizzy Too, most of the time.
Visit site
If you have trim flaps why not use them?

Ballast is ok, but have to get rid of it when on the plane to lift the bow out of the water.

About heavy diesel engine:
The Yanmar 4-cyl is 345 kg and delivers 240 hp,
A Merc 5.7 MPI V8 is 390 kg and delivers 300 hp
- both weights excl. sterndrive.
Admittedly a difference but not that much.

Your Yanmar pushes hard (torque) from 2000-2100 so if there when getting over the hump (starting to plane), I should work.
Change of pitch will of course move the speed/Torque point.
 

SampoSam

Member
Joined
26 Sep 2023
Messages
54
Visit site
Many thanks will remove as much weight as possible then take it out and see how she goes with using trim tabs as well
 

ChromeDome

Well-known member
Joined
25 Sep 2020
Messages
3,543
Location
Commonly in Denmark. Dizzy Too, most of the time.
Visit site
If you source a laser tacho you can kill several birds with one stone.

Get accurate
- engine rpm
- prop shaft rpm
- speed vs. rpm
- speed and rpm when getting on plane
- and engine rpm at full throttle

which all will set basis for an informed suggestion of a propeller.

Thinking about which, Quicksilver's Performance Vent System® (PVS®) popped up in my memory. Does your prop have it?
1707050016800.png

When the rubber plug is removed, the holes vent exhaust around the outside of the prop, allowing the prop to spin up to an RPM in the motor's optimal power band more quickly. Otherwise, on some boats it feels like trying to get your car rolling from a dead stop using third gear.
 

SampoSam

Member
Joined
26 Sep 2023
Messages
54
Visit site
Interesting ? - i will check but don't recall seeing a plug mine is mercury Bravo 1 not Quicksilver so may not be the same ?
 

ChromeDome

Well-known member
Joined
25 Sep 2020
Messages
3,543
Location
Commonly in Denmark. Dizzy Too, most of the time.
Visit site
Interesting ? - i will check but don't recall seeing a plug mine is mercury Bravo 1 not Quicksilver so may not be the same ?
It's all in the name. Mercruiser (inboard) and Mercury (outboard) shared many accessories and even made some for other makes. To support sales to non-Merc customers the more generic brand Quicksilver was used. I believe they tend to brand accessories aimed at Merc by their name now.

The benefit of PVS is that you can play with it and just put the plugs back in if not happy. If you (manage to) drill holes in your prop you won't have that option (drilling in these isn't easy!) unless you get it accurate and buy a set of OEM plugs
 

QBhoy

Well-known member
Joined
11 Mar 2016
Messages
2,612
Visit site
Many thanks that's very helpful. They certainly do seem to be stern heavy boats. I was running a full tank of fresh water ( not sure why ?) which i have now emptied plus i have loads of heavy tools which i will also take off. I am told that you shouldn't need to use trim tabs but it seem logical to help get up on the plane. Also feel weight distribution is important and needs some ballast on bow as so stern heavy. Would appreciate if you could find the prop size as everyone i have spoken to has a different opinion !
Thanks again fir your time
I’ll see what I can find from then. I’m sure we discussed it when he had the boat. It’s seemed well propped for what it was to be fair.
Yeah…tabs help loads to get her going a little better. Come on boost a little quicker too. Just quite important to get them up out the way as you plane, I think. Just to save that lurch they can take, without the passengers knowing what’s going on. Can give a fright to the unexpected person, especially on a boat like that, seating quite aloft and the narrow hull.
About the narrow hull that insists on clever weight distribution and an occasional need for a tab in a wind…yeah it means this…but also means a very good boat in choppy waters. Just the traits of a narrow v hull I suppose.
What do you think your outdrive is ? A bravo one ? Or maybe a bravo diesel x or something? What prop is on it now ? Diameter and pitch ?
 

SampoSam

Member
Joined
26 Sep 2023
Messages
54
Visit site
I’ll see what I can find from then. I’m sure we discussed it when he had the boat. It’s seemed well propped for what it was to be fair.
Yeah…tabs help loads to get her going a little better. Come on boost a little quicker too. Just quite important to get them up out the way as you plane, I think. Just to save that lurch they can take, without the passengers knowing what’s going on. Can give a fright to the unexpected person, especially on a boat like that, seating quite aloft and the narrow hull.
About the narrow hull that insists on clever weight distribution and an occasional need for a tab in a wind…yeah it means this…but also means a very good boat in choppy waters. Just the traits of a narrow v hull I suppose.
What do you think your outdrive is ? A bravo one ? Or maybe a bravo diesel x or something? What prop is on it now ? Diameter and pitch ?
sorry for delayed response. It is a bravo x1 outdrive with 15 1/4 diameter prop with 24 inch pitch and 4 blades
 

QBhoy

Well-known member
Joined
11 Mar 2016
Messages
2,612
Visit site
sorry for delayed response. It is a bravo x1 outdrive with 15 1/4 diameter prop with 24 inch pitch and 4 blades
No worries. Any idea of what kind of top end speed you are getting gps and at what rpm ? Sorry if you’ve already said.
 

QBhoy

Well-known member
Joined
11 Mar 2016
Messages
2,612
Visit site
sorry for delayed response. It is a bravo x1 outdrive with 15 1/4 diameter prop with 24 inch pitch and 4 blades
It’s surely got to be a 1.65 ratio I’d think. That’s what will likely show the most realistic prop slip figures, if I’m assuming some realistic performance and rpm data off the top of my head here. You think your tacho is accurate at 3800 rpm ? Is the spec rpm supposed to be less perhaps ? Early 3000’s ? So she’s definitely a bravo 1x diesel specific outdrive we think ? Does the outdrive say “diesel” on it ? Up the top of the outdrive on one of the decals, there will likely be a stamp saying “1.65r” or “1.50r” or similar. Any way to have a look ?
Although that bravo one propeller you have, can be a great prop on the right boat (for a 4 blade at least), I would be almost certainly confident to say that it wouldn’t have been fitted on that boat when new. Someone has likely added that prop to her at a later date. Could be wrong.
So from here. We really need to know some accurate numbers on gps speed top end and at what rpm. If the rpm spec for that engine is say 3300 rpm, it’s maybe unlikely it will allow you to actually achieve a figure of 3800rpm, by means of a governor or other means of intervention and limitation.
 
Top