28 pitch thru 32 pitch, same speed

Well, here's where I am as far as prop selection goes and I've run into this with most all my power plants over the years... On GPS, my boat runs 73 MPH Period!
If I run a 32 pitch, I run 73 @ 4500 RPM. If I run a 30 pitch, I run 73 @ 5200-5300 rpm. If I run a 28... Well, you know the rest....
The application is a 1989 Arriva 24" open bow boat V bottom with a Bravo 1, 1.5:1 ratio. at what I guess is about 3500-4500 pds. The props are all bravo one 4 blades. The engine is a blown 498 w/ 10 pds boost, good heads and large cam. So, anyway is this what I should expect? It seems to be the same for all the plants I've run over the years. The first was 50 MPHw/a 330 HP 454. The second, 57 MPH the third 63 MPH and now 73 MPH@ approx 900 HP. All with the same results regardless of any prop changes.
Here's my question. Is this what you guys see too? Am I missing something? I guess I should run the 32 pitch as it delivers the same top end @ 4500 RPM rather than spinning 5500 or 6000 for the same top speed. The boat planes instantly no matter what prop. What to do? What to do??

That's pretty damn weird. 28-32 pitch props and they all run 73. Not sure what to think of it. I would say though, do not run the 32. If your only able to turn 4500 rpm's, your lugging the motor too much. This causes a greater chance of developing detonation. Also it's harder on the drive. Run the 30 pitch and let the motor rev out a bit more. Easier on motor, easier on drive and gives a better mid range punch.
Darrell.

Basically your engine has the same HP at 4500 as it does at 5300. This is typical of a large CID blower motor. Run the 30 for reasons above. I might start looking at X-dimension. 3 inches below bottom is where Id like to be.

Why not try a half inch smaller prop with the 32 pitch or even a 1/4 inch smaller. Pitch dictates the forward speed/rpm but the smaller circumfrence should allow more rpms with the same pitch. You might loose just a little out of the hole. But, I think you'll have enough HP to still launch hard.

Try using the trim button, and if you have tabs raise those too. LOL. Just joking btw.
Sounds like your boat doesn't want to move. Got any pictures , especially the bottom along as mentioned above how deep your drive is ?
You sure the Bravo style prop is what your boat wants ?

Try using the trim button, and if you have tabs raise those too. LOL. Just joking btw.
Sounds like your boat doesn't want to move. Got any pictures , especially the bottom along as mentioned above how deep your drive is ?
You sure the Bravo style prop is what your boat wants ?
There's a thing called a trim button?
:D :D :D :D :D :D
The trim button is my happy place, I'm all about it. Anyone who wants max speed has his finger on the trim button constantly. I like it so much that I moved one onto my throttle, right in my hand!!!!
All speeds taken by GPS:mad:

Basically your engine has the same HP at 4500 as it does at 5300. This is typical of a large CID blower motor. Run the 30 for reasons above. I might start looking at X-dimension. 3 inches below bottom is where Id like to be.
I've always been very suspicious that my drive was way way way too low.
How do I take my measurements? Thanks.

It takes X amount of HP to run X speed. The top speed will stay the same as long as your engine makes comparable HP at the different RPMs, and most blower motors and many milder motors do. The exception is a high strung motor with big heads,and large cam, giving a peaky power band, those motors tend to react quite a bit to RPM changes, and the speed will react accordingly. If you are happy with the holeshot, run the biggest prop and keep the revs down. TIMINATOR

Well, here's where I am as far as prop selection goes and I've run into this with most all my power plants over the years... On GPS, my boat runs 73 MPH Period!
If I run a 32 pitch, I run 73 @ 4500 RPM. If I run a 30 pitch, I run 73 @ 5200-5300 rpm. If I run a 28... Well, you know the rest....
The application is a 1989 Arriva open bow boat V bottom with a Bravo 1, 1.5:1 ratio. at what I guess is about 3500-4500 pds. The props are all bravo one 4 blades. The engine is a blown 498 w/ 10 pds boost, good heads and large cam. So, anyway is this what I should expect? It seems to be the same for all the plants I've run over the years. The first was 50 MPHw/a 330 HP 454. The second, 57 MPH the third 63 MPH and now 73 MPH@ approx 900 HP. All with the same results regardless of any prop changes.
Here's my question. Is this what you guys see too? Am I missing something? I guess I should run the 32 pitch as it delivers the same top end @ 4500 RPM rather than spinning 5500 or 6000 for the same top speed. The boat planes instantly no matter what prop. What to do? What to do??
What kind of speeds are you looking for from that hull?

What kind of speeds are you looking for from that hull?
Simple, as much as possible. But I realize I may be at the limit or close. I just don't know.

The boat has shown the same characteristics no matter what engine he's run. The problem is in the boat and setup. I just pulled out 5 different dyno sheets on various blown engines ranging from 509 CI to 572 CI. Everyone made at least 100 HP more at 5300 than at 4500. It is possible that their is a mismatch in his engine combo.... except that all engines react the same way.
Look at the bottom, look for hooks in the running surface and strakes. Run a straight edge off the bottom with the propshaft parallell with the bottom and measure how far below the bottom the propshaft is.
It sounds like you are not getting more lift as the speed increases and it is hitting a wall at 70.
EDIT: One thing that sticks out is you say "large cam".... how large and what are "good heads"?

Your Arriva is the older style and it may have a hook that's causing it hitting the wall @ 73 . I wouldn't push that boat much faster ;) . The newer Arriva was tooled and refined to
be a better performer
http://www3.telus.net/spectrasonly/1996%20Arriva.jpg

The application is a 1989 Arriva open bow boat V bottom
BTW, I always liked the look of the Arriva. There was just a 90 for sale here in San Diego. A buddy was looking at it but couldn't come up with the cash in time. As for measuring the prop shaft; measure from the bottom of the keel (I'm assuming there is no pad) to the center of the shaft. Remember, these boats were set up for pleasure cruising, and good on plane performance, not top speed. Because of this the drives as set quite deep.My guess is that it's buried. Thats why even with a big prop, the boat still jumps on plane
Darrell.

I've always been very suspicious that my drive was way way way too low.
How do I take my measurements? Thanks.
OK, propshaft is 9-10" below the bottom of the V.

OK, propshaft is 9-10" below the bottom of the V.
HOLY smokes! that thing is buried. On a vee like yours, you would want about 6-7" below, for performance. All of that drive in the water is really holding you back. If it were me, I would go with a 3" shortie, then if it's TOO short, you can add a spacer for cheap. I've seen ya on the oso site also, try the ads there, ya may be able to pick up a used one for a decent price. If ya need a hand I'm only an hour down the road. Sometimes an extra set of hands really helps.
Darrell.

Your Arriva is the older style and it may have a hook that's causing it hitting the wall @ 73 . I wouldn't push that boat much faster ;) . The newer Arriva was tooled and refined to
be a better performer
http://www3.telus.net/spectrasonly/1996%20Arriva.jpg
I was always under the impression the earler Arrivas were a better tooling and stronger manufacture due to the fact that Bayliner bought them out in the early 90's. I was told quality and strength were compromised on the later ones because of this. The hull as I compared it never changed only the manufacturing quality suffered later?????:confused:

HOLY smokes! that thing is buried. On a vee like yours, you would want about 6-7" below, for performance. All of that drive in the water is really holding you back. If it were me, I would go with a 3" shortie, then if it's TOO short, you can add a spacer for cheap. I've seen ya on the oso site also, try the ads there, ya may be able to pick up a used one for a decent price. If ya need a hand I'm only an hour down the road. Sometimes an extra set of hands really helps.
Darrell.
I always felt as though it had a parking brake on when I gave up the throttle. I have to trim this boat so far up it's unbeleivable. What would be the best overall depth considering stability as well as speed? At what point do you give up the excellent handling characteristics of this boat? I will post pics for you all to look @ later today, please all of you, take a look. Thanks
Darrell, I appreciate the offer as I've never pulled a lower and have only pulled the entire drive too many times too count.....

Here You Go, The Hull!!!!

I was always under the impression the earler Arrivas were a better tooling and stronger manufacture ?????:confused:
I'm not so sure about that . The newer ones were rated for more HP .
The earlier ones were rated for the 330 BB as max :idea: .

What would be the best overall depth considering stability as well as speed? Thanks
Your drive is definitely too deep down as dmoore mentioned . It was meant to be a runabout , not a speed demon ;) . 7" would be much better , and you could go shorter .
BTW , I like the older models compared to the new ones that are a little overdone in styling .

Put stock power in it, sell it, and get a boat that would appreciate that motor more ?
Something to think about.
Raising the drive enough and doing some bottom work may not give you what you are looking for. It may....but this will be a road never travelled unless you find someone with the same exact boat that has done this before.
But, some people like to go down untraveled roads and enjoy the challenge even if the ultimate result ends up be nothing.
Depends on you.

Put stock power in it, sell it, and get a boat that would appreciate that motor more ?
Something to think about.
Raising the drive enough and doing some bottom work may not give you what you are looking for. It may....but this will be a road never travelled unless you find someone with the same exact boat that has done this before.
But, some people like to go down untraveled roads and enjoy the challenge even if the ultimate result ends up be nothing.
Depends on you.
You are correct in what you say. I've built the motor for my "next hull" and the fact that it is in this one is only due to it's the boat I've had for 12 years. I'm looking forward to a 29 Ft or so next and am just starting to look @ hulls to transfer this motor into. But for now, it's what I'm running and I'm wondering what can be done for top speed. I am not willing to do ANY hull work on this boat. Again what should I be looking for regarding drive height? And yes, I own the fastest Arriva ever built and I'm sure of that. HAHAHAHA!!!!:D :D :D :D :D

I always felt as though it had a parking brake on when I gave up the throttle. I have to trim this boat so far up it's unbeleivable. What would be the best overall depth considering stability as well as speed? At what point do you give up the excellent handling characteristics of this boat? I will post pics for you all to look @ later today, please all of you, take a look. Thanks
Darrell, I appreciate the offer as I've never pulled a lower and have only pulled the entire drive too many times too count.....
In general, what speed increase can one expect from increasing drive height each inch? Say maybe from 10" to 7" or 6"? And what would the optimal drive height be?

Here You Go, The Hull!!!!
In your first picture the drive is not parallel with the keel. That will give you a lower x-dim measurement. It is critical to be correct in all your measurements.
If it is 9" below the keel a 3" shorty wont help you a lot. Single vee's do not like the Imco style lower with the crescent above the bullet. Especially heavier ones like yours. Your boat requires a lot of trim even if the x was higher. When you do that the front of the bullet acts like an anchor and creates a ton of drag.
Not spamming, but we modify the nose on Imco's all the time to correct that problem.

In your first picture the drive is not parallel with the keel. That will give you a lower x-dim measurement. It is critical to be correct in all your measurements.
If it is 9" below the keel a 3" shorty wont help you a lot. Single vee's do not like the Imco style lower with the crescent above the bullet. Especially heavier ones like yours. Your boat requires a lot of trim even if the x was higher. When you do that the front of the bullet acts like an anchor and creates a ton of drag.
Not spamming, but we modify the nose on Imco's all the time to correct that problem.
What do you find the effect to be when installing the nose cones? I've heard good and bad on that. What about a nose cone on the standard Bravo? Any help on my application?

In general, what speed increase can one expect from increasing drive height each inch? Say maybe from 10" to 7" or 6"? And what would the optimal drive height be?
xx

Here you go !
IMHO, this is a great price and a fast hull.
http://www.speedwake.com/upload/show...0&pagenumber=3

OOps. Double posted. Doh.

What do you find the effect to be when installing the nose cones? I've heard good and bad on that. What about a nose cone on the standard Bravo? Any help on my application?
It's not a nose cone, rather a complete modification to the gear housing. On a 25 Daytona OPEN BOW (I know it's a cat) with a 540 normally aspirated BBC, we picked up 9 to 10 mph. The drive is mounted lower on an open bow because it needs more trim.
On a 24 vee we picked up 8 mph.
The key is that the gain is larger the deeper the drive. This is strictly on an Imco (Speedmaster style) drive.
Installing a nose cone an a standard Bravo helps feed the prop and will increase speed slightly. There are many variables as to how much you will gain. The earlier Bravo gear cases (88 & 89)respond better than the newer ones. Drive height, hull design, horsepower, etrc. are all factors. There also different nose cone manufacturers and some are bettrer than others.

Did your boat have an alpha at one time? That hull has many lifting strakes at the bow, seems like it would have some good lift if they ran most of the way back. Just for grins try a merc. revolution4 . Last I heard they only go up to 27" though. But it might steer you in the right direction. The imco style lower wont work on a non trim sesitive v-hull. Further, a 3" shorter anything probably wont do much. If you were going to move the drive up, I would go all the way to the top of the transom relief 5-6" up maybe.

Is there any chance that trim tabs might raise my transom @ WOT enough to make any difference or would they just create more drag? I've never needed any as this boat planes instantly no matter what prop you run and there is zero chine walk @ 73 MPH.

Water brakes wont help

Did your boat have an alpha at one time? That hull has many lifting strakes at the bow, seems like it would have some good lift if they ran most of the way back. Just for grins try a merc. revolution4 . Last I heard they only go up to 27" though. But it might steer you in the right direction. The imco style lower wont work on a non trim sesitive v-hull. Further, a 3" shorter anything probably wont do much. If you were going to move the drive up, I would go all the way to the top of the transom relief 5-6" up maybe.
The strakes make almost a full run to the rear.

Try to get a hold of a 27 rev4. I know it does not have enogh pitch but it may trade some possitive bow lift for total foward motion. Meaning that if you can get more of the front of the boat out of the water it may begin to build more speed. Even though some of your horsepower is being used to lift the bow of your boat rather than push it foward. The trade off for bow lift with this type of prop may outway the lack of foward thrust. If this works, it may only yeild you 3-6 MPH anyway. Get a TUNNEL.

Try to get a hold of a 27 rev4. I know it does not have enogh pitch but it may trade some possitive bow lift for total foward motion. Meaning that if you can get more of the front of the boat out of the water it may begin to build more speed. Even though some of your horsepower is being used to lift the bow of your boat rather than push it foward. The trade off for bow lift with this type of prop may outway the lack of foward thrust. If this works, it may only yeild you 3-6 MPH anyway. Get a TUNNEL.
6 MPH I'm lov'n it man!!! As far as a tunnel? Who makes the one that I can go to Catalina with 30 miles offshore and feel confident in 4 ft swells? Please tell me because I would love to find it in under 30 ft that can handle offshore running........:confused: :confused: :confused: :confused:

Ask cats and tunnels forum

Hell, I ain't yer buddy, but I know a pile a crap when I hear about one. Go Rotary...Yer friends will envy yew...:)