could it be propped wrong?

[jere1972]

I have a 95' Renkin seamaster 2688, the boat originally had a 7.4L Yamaha hydradrive, I repower the boat with a 91 7.4L merc/Bravo 1 1.50 that i pulled from a damaged 23' Cuddy, the guy told me the boat used to run 60mph before damaged,
the merc came with a 23" pitch mirage not sure on the dia, installed in my Renkin, the boat seemed to have difficulties getting to a planning state. with a top speed on relative calm seas 1' or less @ 28mph, I purchased a used but never used ss Mirage 19", she gets up on a plane great , top speed seems to be around 33-34 (GPS), on a calm day seas @ 1' or less, running the 23 my rpms would barely hit 4k maybe trimmed out, with the 19 I can hit 4600 trimmed out with no problem, I normally run around 3500 about 25-26 mph, I never had a boat this heavy or long, so not certain if I'm running where I should be, the yamaha had a 19", but it feels to me I should have more top end, with the 19 it makes no difference if I have 2 people on board or 6 people, she runs out the same, the hole shot now seems good but I'm thinking my top end is lagging. but I'm comparing things as to how my 20'ran with a johnson 225, which would top out around 56 running a 17"

 

[QC]

Re: could it be propped wrong?

pulled from a damaged 23' Cuddy, the guy told me the boat used to run 60mph before damaged,

I kinda think he stretched the truth a little . . . What boat and model etc did it come from?

Have you verified your tach? Could be right as is, basically I think your biggest issue is that this prop and drive actually is for a faster boat. These are really designed for 50+ and you are not going to get close to that with 300 - 310 horsepower. The hole shot sounds good, but I am thinking you need a larger diameter and also you should be able to go up in pitch a little based on the RPM. Both may help bring down your slip numbers which seem high to me.

Edit: Ooops, added "not" to the speed sentence. Makes a big difference . . .

 

[Bondo]

Re: could it be propped wrong?

I have a 95' Renkin seamaster 2688, the boat originally had a 7.4L Yamaha hydradrive, I repower the boat with a 91 7.4L merc/Bravo 1 1.50 that i pulled from a damaged 23' Cuddy, the guy told me the boat used to run 60mph before damaged,
the merc came with a 23" pitch mirage not sure on the dia, installed in my Renkin, the boat seemed to have difficulties getting to a planning state. with a top speed on relative calm seas 1' or less @ 28mph, I purchased a used but never used ss Mirage 19", she gets up on a plane great , top speed seems to be around 33-34 (GPS), on a calm day seas @ 1' or less, running the 23 my rpms would barely hit 4k maybe trimmed out, with the 19 I can hit 4600 trimmed out with no problem, I normally run around 3500 about 25-26 mph, I never had a boat this heavy or long, so not certain if I'm running where I should be, the yamaha had a 19", but it feels to me I should have more top end, with the 19 it makes no difference if I have 2 people on board or 6 people, she runs out the same, the hole shot now seems good but I'm thinking my top end is lagging. but I'm comparing things as to how my 20'ran with a johnson 225, which would top out around 56 running a 17"

Ayuh,.... Welcome Aboard,... I think ya got it 'bout Right,...

I can't believe a BBC wouldn't be Happy, toppin' out at 4600 rpms... that's 'bout Peak Power...

If ya dropped to a 17", I believe it'd spin Too high...

I also think a 21" would be Too tall, droppin' the rpms too far...

 

[emilsr]

Re: could it be propped wrong?

4600rpm is where you want to be. Pitch isn't the problem here unless your tach is off. I'd verify that before going any further.

Slip is VERY high (or the tach is off). Is what you have a Mirage or a Mirage +? If it's the standard Mirage, probably not the best choice for that boat....but again, verify your data gathering devices before playing with props.

 

[jere1972]

Re: could it be propped wrong?

I'm not certain on the mirage, it just says mirage, I picked it up off ebay, however I don't know if I can go much larger in Diameter, based on what clearence I have left, I know the 23p" worked her to much, and 19p" seems like she wants more, I just started looking into what prop slip is, and yep I agree there is a problem, the tach is new, and shows the same as the old, I replaced it because it would stick at times, I don't think there is a problem in the mid RPM range but I really don't know, how ever going from 3500 to 4600 there is only around a gain of 5-6mph, could there be something wrong with the way the package was installed, I took great care with alignment, but the keyhole is where it is, and could not be cut lower, I know with my other boat, lowering the outboard 1" made a world of difference, but can't do that with a sterndrive I know, would a Fin on the drive help with the prop slip, at it's max there is no issue with turns she turns pretty well, I just don't know if this is just what it is on a larger heavy boat and I'm expecting to much. I'm still unclear as to what actually causes prop slip, but with the high costs of props I don't really want to develope a stock pile,
Oh and after I purchaced the engine and drive, someone did tell/warn me these were made for the go fast hulls, and I should have looked for a Bravo 3, but @ the time I was begging and was happy to get what i got for my $800 complete, used systems in that size range in my area seemed to be very hard to find,
as to what this came out of, I don't recall the make, but I do remember thinking that 454 was way over kill, it was a low profile steamlined hull but had a cuddy, light boat.

 

[Bondo]

Re: could it be propped wrong?

Ayuh,... Considerin' the drive, 'n prop came from a Go-fast hull, 'n it's now in a bigger, heavier hull,...

I'd think ya might need to ditch the mirage, 'n go with a big eared cruiser type prop...

 

[QC]

Re: could it be propped wrong?

Ayuh,... Considerin' the drive, 'n prop came from a Go-fast hull, 'n it's now in a bigger, heavier hull,...

I'd think ya might need to ditch the mirage, 'n go with a big eared cruiser type prop...

That's what I was trying to say. Left out an important word. Doh :facepalm:

 

[emilsr]

Re: could it be propped wrong?

I'm not certain on the mirage, it just says mirage, I picked it up off ebay, however I don't know if I can go much larger in Diameter, based on what clearence I have left, I know the 23p" worked her to much, and 19p" seems like she wants more, I just started looking into what prop slip is, and yep I agree there is a problem, the tach is new, and shows the same as the old, I replaced it because it would stick at times, I don't think there is a problem in the mid RPM range but I really don't know, how ever going from 3500 to 4600 there is only around a gain of 5-6mph, could there be something wrong with the way the package was installed, I took great care with alignment, but the keyhole is where it is, and could not be cut lower, I know with my other boat, lowering the outboard 1" made a world of difference, but can't do that with a sterndrive I know, would a Fin on the drive help with the prop slip, at it's max there is no issue with turns she turns pretty well, I just don't know if this is just what it is on a larger heavy boat and I'm expecting to much. I'm still unclear as to what actually causes prop slip, but with the high costs of props I don't really want to develope a stock pile,
Oh and after I purchaced the engine and drive, someone did tell/warn me these were made for the go fast hulls, and I should have looked for a Bravo 3, but @ the time I was begging and was happy to get what i got for my $800 complete, used systems in that size range in my area seemed to be very hard to find,
as to what this came out of, I don't recall the make, but I do remember thinking that 454 was way over kill, it was a low profile steamlined hull but had a cuddy, light boat.

Your B1 drive will work fine if the prop is at the proper height.

With the drive trimmed level with the bottom of the boat, what is the distance between the center line of the prop shaft and the bottom of the hull? If this is less than about 6" or so this could be causing some of your prop slip. They do make spacers to get the prop deep enough.

 

[jestor68]

Re: could it be propped wrong?

Solas makes a Rubex L3 SS 16 X 19 to fit your Bravo 1 drive. The extra blade area may be just the ticket for your application, since your prop is a 15.25 diameter(I think).

The Rubex L3 is designed for heavy loads and high horse power applications.

 

[jere1972]

Re: could it be propped wrong?

I stop by the boat on may way home this evening, and check the dimensions, thanks for your help guys,

Guess I'm showing my ignorance here, guess I thought a prop was a prop, just pitched different, what would make the mirage not a good choice, what is the big eared prop???? is that alum??
the Boat in jester68 pic is just like mine

 

[QC]

Re: could it be propped wrong?

I can't tell you why, but larger, heavier, slower boats do best with more blade surface, so you want bigger "ears" whether it be by diameter, or shape, or both. I guess it is surface area vs. boat weight.

 

[emilsr]

Re: could it be propped wrong?

I stop by the boat on may way home this evening, and check the dimensions, thanks for your help guys,

Guess I'm showing my ignorance here, guess I thought a prop was a prop, just pitched different, what would make the mirage not a good choice, what is the big eared prop???? is that alum??
the Boat in jester68 pic is just like mine

There are MANY different "flavors" of props; small ear, big ear, 3, 4, 5 or more ears....lots of different options for different applications. The reason I say the Mirage + would probably be a better option for you is that it has more blade area (and more cup) than the old style Mirage.

I'm not familiar with the Rubex that jester mentioned, but I do know the Merc Bravo I pretty well and it seems to work well where the prop tips are at or near the surface of the water. That may be another option, but a spacer is a little cheaper than a new SS prop (although not much).

Check your prop depth and go from there.

 

[QC]

Re: could it be propped wrong?

I would argue your experience with single Bravo 1's is with lighter and significantly faster boats. There is a reason they made Bravo 2's for larger cruisers, which is deeper and allow larger diameter props. And now they are almost 100% Bravo 3s

My guess is if he brings that Mirage any higher ( I think that is what you suggest) that it will slip more, not less.

 

[emilsr]

Re: could it be propped wrong?

I would argue your experience with single Bravo 1's is with lighter and significantly faster boats. There is a reason they made Bravo 2's for larger cruisers, which is deeper and allow larger diameter props. And now they are almost 100% Bravo 3s

You'd think so given my last 2 boats, but I'm a boater first, a performance boater second. 4 boats ago I had a heavy cruiser, so they're not exactly foreign.

The BIII would be a better option, but I don't see the OP switching drives at this point. The B1 will handle a larger diameter prop than he's running (up to 16" I think) so there's some room to play there.

If I remember correctly (which, at my age, is suspect) the Hydradrive has different dimensions than the B1....so it's possible the prop is running too high in the water if they mounted it in the existing transom holes. We'll know more after he measures it. 4-5" prop depth is great on a high powered, single engine go-fast.....not so great on a heavy cruiser. As mentioned, I'd be looking for something in excess of 6" there (7-8" would be even better). If he's under 6" then a large diameter prop is just going to break the surface and not produce much thrust (but a really sporty roostertail).

 

[QC]

Re: could it be propped wrong?

OK, I thought you were recommending that he try and run it higher. Yes, too high could produce what he is seeing here too. I would want rounder and larger diameter blades. Something you would run on older, single screw, Alpha driven cruiser.

Still not sure what you mean by a spacer

 

[emilsr]

Re: could it be propped wrong?

OK, I thought you were recommending that he try and run it higher. Yes, too high could produce what he is seeing here too. I would want rounder and larger diameter blades. Something you would run on older, single screw, Alpha driven cruiser.

Still not sure what you mean by a spacer

Lower is better, at least in this case.

Here's one brand of Bravo drive spacer (there are several): Latham Marine

Using these you can lower the prop shaft up to 3". I've never seen them used on anything other than a performance boat, but there's no reason you couldn't.

 

[QC]

Re: could it be propped wrong?

Got it. I still thought you were talking about going up, and didn't make any sense to me

 

[emilsr]

Re: could it be propped wrong?

Got it. I still thought you were talking about going up, and didn't make any sense to me

If it makes you feel any better, going up doesn't make sense to me either on his boat. On mine I'd like to go up about 1", but they don't make a space remover that I know of....and shorty drives are expensive. :lol:

 

[jere1972]

Re: could it be propped wrong?

checked what emilsr suggested, the prop shaft centerline is 8" below the lowest part of my transom, also this is the model # of my prop 48 13700 A41 19p, all it states is Mirage, there seems to be around 3/4-7/8" clearence between the prop and the gearcase , the Hydra drive key actually was a bit larger then the Bravo, if I recall only the top 2 stud holes lined up,the Gimble assembly was much bulkier, we had to replace the transom wood so we glassed in the outer skin and made a new cut out using the original top hole as a height guide, both the bravo and the Yamaha were very close in dimensions with respect to the top stud and the antivent plate

 

[emilsr]

Re: could it be propped wrong?

checked what emilsr suggested, the prop shaft centerline is 8" below the lowest part of my transom, also this is the model # of my prop 48 13700 A41 19p, all it states is Mirage, there seems to be around 3/4-7/8" clearence between the prop and the gearcase View attachment 178129, the Hydra drive key actually was a bit larger then the Bravo, if I recall only the top 2 stud holes lined up,the Gimble assembly was much bulkier, we had to replace the transom wood so we glassed in the outer skin and made a new cut out using the original top hole as a height guide, both the bravo and the Yamaha were very close in dimensions with respect to the top stud and the antivent plate

Scratch that as a possible problem. 8" is good.

Clean bottom? Nothing disrupting water flow on the keel?