Changing drive

[Rick Stephens]

AllDodge's list is all of about an hour's worth of tinkering. Taking the prop to a shop, or even shipping it is easy. Replacing the lower, or the entire leg, and finding out your shift cables were misadjusted seems maybe extravagant. Guess it would make a good 'what's in your wallet' commercial.

 

[ericcarr2000]

Ok I just got done pulling the drive off, taking the 2 inspection covers off... I didn't notice any metal shavings or anything strange in the fluid other than some h2o that might have dropped there while taking them off and moving the drive around. So I guess I'll just put a bravo 3 lower unit on her and see what happens...

 

[alldodge]

Have a close look at your shift bracket and linkage. Any slop in anything you have seen. My guess is you did drain everything and nothing abnormal, right?

 

[HT32BSX115]

Ok I just got done pulling the drive off, taking the 2 inspection covers off... I didn't notice any metal shavings or anything strange in the fluid other than some h2o that might have dropped there while taking them off and moving the drive around. So I guess I'll just put a bravo 3 lower unit on her and see what happens...

Howdy,

Changing to a Bravo III drive will absolutely result in better holeshot performance in your size of boat.

A 2.00:1 ratio would be right for that boat, and you should probably start with a 24p propset. The boat will definitely come out of the hole MUCH quicker but you'll probably lose some top speed.

But, having said all of the above, I am going to agree with everyone else here. You need to determine what your original problem is before spending money on a new drive.

Regards,


Rick

 

[alldodge]

See the comment all the time about probably loosing some top end, but have seen nothing to justify it. Agree that you can loose some top end when your starting to reach 50mph, but even that OSO has boats using the B3's at over 70mph

 

[harleyman1975]

It seems like you have money so why not have a pro look at the things that All Dodge suggested? Can you imagine how disappointed you would be next spring if you did all this swapping of parts and it still was "popping out of gear"? Could be something as simple as a spun hub in the prop. (less than $25 to fix that)

 

[alldodge]

So long as no metal is found and the shift linkage on the drive shifts solid with the detent ball and spring, I don't see it as a drive issue. It would have to be something else in the cable to throttle linkage

 

[52FordF2]

Have you check the weight of the boat? It could be holding water somewhere, making it harder for it to get up on the plane.

 

[ericcarr2000]

You know I thought about taking it to a weight station upon pulling it out for the winter...

 

[ericcarr2000]

How would I loose some top end speed by switching to the 3? I know the bravo 1 I currently have is probably the original one due to all the pitting and damage on the casing. Trust me I'm not rich by any means, I just want to nip this in the bud and maybe even kill 2 birds with 1 stone.

 

[HT32BSX115]

How would I loose some top end speed by switching to the 3?

For one thing, 2 propellers result in exactly double the drag of one propeller. It's especially more pronounced at high speed. So maybe it's more accurate to say there's a slight loss of propshaft HP (to rotational drag) which may make up for the slightly lower slip from 2 props.....

The reduction is claimed to be 3mph according to some.

In my '87 Four Winns 211 Liberator I experienced about 3 mph reduction going from a similarly powered single prop 460 (340 crankshaft rated HP) King Cobra drive with a SS prop that would do about 60 mph flat out...........TO a (1997 model) 454 (330 crankshaft rated HP) + Bravo III, I installed in the same boat.

The 460/King Kobra however was a REAL DOG outta the hole.............(even when the boat was brand new)

With the Bravo III, the large increase in low RPM thrust results in a hole-shot that is nothing short of spectacular!! AND at cruising (planing) speeds, I noticed a slight reduction in fuel flow.

Although you certainly need to determine exactly what your problem is with the boat now, I think it's absolutely worth going to a "DUO" prop type drive. Just understand that the drive and props will be more money.

 

[ericcarr2000]

No kidding?.... Then maybe I need to rethink this then because with my current setup, 330 hp with the bravo 1 I can only get her up to about 35 mph. What if I were to change to a different gear ratio like a 1.81:1?

 

[thumpar]

It is not a matter of gear ratio. Since you are asking about not being able to plane I am guessing that you at one time could plane out. You need to figure out what changed.

 

[Rick Stephens]

It is not a matter of gear ratio. Since you are asking about not being able to plane I am guessing that you at one time could plane out. You need to figure out what changed.

I'd bet heavy boat (waterlogged) or fouled bottom or both.

 

[HT32BSX115]

No kidding?.... Then maybe I need to rethink this then because with my current setup, 330 hp with the bravo 1 I can only get her up to about 35 mph. What if I were to change to a different gear ratio like a 1.81:1?

Well, you might be able to use a 1.81:1 drive.....IF IT'S A Bravo III.............................

My 454/Bravo III came out of a 24ft Bayliner cuddy. It's also a 1.81 and it had 24p props on it. I obtained a 26p propset because I was bumping the rev limiter at about 4700-4800 RPM.

With 26p props, I was able to get about 57 mph at 4600 lightly loaded on a slight chop. Your boat probably weighs quite a bit more than my 21ft Four Winns.
(Mine is approx 4100lbs... 2900--boat, 1200--engine/drive)

If you did get a 2.00:1 drive, you could probably start with 24's and possibly go to 26's.


Your Bravo I is a 1.5:1 isn't it?

Let me also add that your 250 Sundancer weighs in at around 6900 lbs doesn't it?


That kind of weight isn't going to go 60 mph with 300 (prop) HP.

Even with a Bravo III, you might still get around 35-40 for top speed. And because of the much higher weight, I think you'd need either a 2.00:1 or even a 2.20:1 Bravo III with a stock 454

 

[ericcarr2000]

According to the specs, it weighs 5200 lbs dry.

 

[alldodge]

If you have a 1.5 ratio B1 turning a 19 pitch prop and WOT is 4600 your slip is 36 percent, something isn't right
If your ratio is 2.0 then that gets you into the 15 percent range which would be where you would want to be and a bit less if possiable

 

[ericcarr2000]

What do you mean by my slip is 36%?

 

[alldodge]

What do you mean by my slip is 36%?

I don't know what prop pitch or drive ratio your using so I plugged in some numbers based on some assumptions. Here is a link to bblades prop calculator
http://bblades.com/propeller-slip-calculator/

So using the numbers mentioned above it comes out to 36%

 

[mr300z87]

I have the exact same boat 454/7.4 B1 combo, see her project thread in my signature, it is still a project and I have not had it on the water for sea trial yet so I can not give you any performance data. Just for informational purposes i thought I would share what I know, mine came equipped when I received it with the original 1.5 ratio B1 drive and an aluminum 17P prop. According to the info I found on Sea Ray's web site it came from the factory with a 17P stainless steel Mirage Propeller. I am hoping to see decent performance from this boat but I know it will not be a rocket by any means. I actually posted one of you threads a while back asking about your boats performance.

I do have some experience with my friends boat a 1989 SR Sundancer 250 his is equipped with 350 (260HP) and 1.5 ratio Alpha drive, I do not know the pitch of the prop. His boat (when running: search my user name for that thread) although was kinda a dog out of the hole, planned out nicely and cruised at 3000RPM about 23-25 MPH. I was never on it for a WOT run since the SEI drive was still getting broken in. Then water in oil and big mess. I can say that I don't think I would want a boat like ours with a 260HP small block.

As everyone is saying before you buy anything fix the problem first. Sea Ray made of ton of these boat and it should perform adequately with the 7.4L B1 combo. Lastly although the cost of a B3 is about the same as a B1 the prop sets are big dollars just go on any site that sells props and see for yourself.