Proplems

[Chops]

Switched my 18 2+3/Merc 260 from Merc Type I drive with a 17P Vengence to a Bravo I with a Mirage 21P. Also added around 30+HP, took 70 LBS (net) out of the back and stuck the battery in the nose.
Net gain: a big zero so far. I used to turn around 4400 at WOT with the 17P to put me in the low 60's. Now with the 21P I turn around 3500 for the same top speed. This makes sense- approx 200 R's per inch is the rule, right? But what about my weight reduction and HP gain? This has no effect? I thought 21 would be about right for the mods.
The Bravo drive itself has some interesting effects too. In a hard left turn at criuse (doesn't everyone do that?) with anyone in the left seat I can pitch the boat up near 90 degrees like it's gonna slip all the way over or something. Trim and the tab adjustments might fix this, right? And don't come off plain too fast with anyone in back or a couple of gallons will wash right over their shoulders.

Any hints?

It's not a boat, it's an adventure.

[Moody Blu']

I can pitch my boat to 90degrees with the volvo drive.you couldnt do that with the alpha?????hmmmm......
as for the back wake rolling over the back of the boat. did you take into account what the stock drive weighed and what the bravo drive weighed? the bravo seems bigger, heavier even? maybe the X dimension is to high?-I have no clue just guessing-

[oldLenny]

Bravo One to an Alpha/Merc 1,is about 35 LBS different by my calc's. Not much, about the same as a battery. As for standing up at 90 degrees in a hard carved turn, don't they all do this?...at least give or take a few degrees and the panic factor, very close to that?
I would like to know how far the Bravo sits underwater as opposed to the Merc 1. Sounds like the long shaft outboard on the short shaft transom scenario. (Added drag as well)
Many boats need a "bit of extra help" when throttled back in a hurry. Doesn't a quick punch of the throttle diminish the following sea problem? The extra horsepower added was based on what HP you had to start with. Do you know what that was? The engine in this 18' is a ???what???

Low sixties in an 18 with a 17" pitch has got to have some VERY low slip figures with a 4400 RPM calculation doesn't it? everyone/anyone...???

[BigGrizzly]

Bet the bravo has a different gear ratio and larger surface area . put a smaller pitch prop on it. maybe a 19

Randy

[Chops]

Len- The Bravo I upper and lower do weigh almost 35LBS more. However, that weight increase was calculated in my overall 70LB reduction at the back of the boat. As I have not changed the transom at all the X dim is the same but the driveshaft to propshaft dim may be longer on the Bravo. The motor is a Merc 260 with minor hop-ups. And yes, juicing the throttle a second as you level off plane does stop the wash-over (which BTW actually comes from this this weird fountain that the drive shoots up about that time). I could be wrong about the low 60's, could be high 50's.

Thanks

[GEOO]

Chops,
Move the battery back. To go fast you need to lighten the bow up as much as possible. This may cause a little porpoiseing at low speeds, but the boat will be able to run with less boat in the water, less drag, faster.
The leaning of the boat is normal.
Does the Mirage prop have a larger diameter? What is the gear ratio of each drive?
Did you try the 17" on the Bravo yet?
GEOO

[Chops]

GEOO- My Bravo is 1.5:1 same as Merc I. Mirage 21 is same dia as Vengeance 17 which I sold before running it on the Bravo (unwise I guess). Hopefully making a purchase of used Vengeance 19 next week.

Thanks

[oldLenny]

If you are "shooting a fountain" when coming off a plane,...I wonder if the drive is staying close to the hull/transom. Also when turning hard, slowing down, and such. When you back up does the lock kick in? There is no lift and cavitation,...is there?. Why does it shoot a fountain? I think the lock is not hanging onto things and the drive is succumbing to the forces of water and leaving the hull into maximum positive trim.

Or not... I am not educated enough in these things to actually offer any "REAL" advise but that was my $.02...Lenny