Rdegeo4140

Thanks for the input "blown formula"
May be so. I've got more than a grand invested in this 22"Bravo.
I have plenty of bow lift, it just seems out of balance when jumping wakes or choppy water.
With the 350/260hp alpha I turned a 16x16 alum prop. Topped out around 37mph(paddle wheel). Now I'm getting about 53 mph(gps) @ 4300rpm.
My biggest problem is lack of experience with this power. I'm not sure how far to trim out drive, tab down, etc.
Does porposing slow or stop at top speed? I was always told not to allow it.
But the main issue remains that the boat with 350/260 alpha weighs 4300#'s. 133 gallons of gasoline = 798#'s, 2 people plus equipment = 500#'s plus new engine package added 258#'s. The grand total is close to 6000#'s. With the bow high she slams down amidship.
I'm hopeful it will get better w/ experience.
Thanks Again
Happy Captain Bob

ursus

The 250 lbs you added in the new engine package is not any different than haveing someone sitting in a rear seat with the old package so did the boat act this way if you had guest sitting at the back with the old engine, probably not, I doubt if weight is your problem.

The hull you have was not designed for this much power and so it has a lot more bow lift built in to plane at a slower speeds and lower power.

To run this fast you need to add a lot of stern lift to compensate either with tabs as you have done or with a cleaver prop as mentioned here or both.

Trim the tabs and drive till it smooths out not for highest speed you may have to run 1-2 mph slower but this is the compromise for takeing the hull beyond its design speed. If you add enuff weight to the bow to do this the boat will be that much lower in the water and you will lose the 1-2 mph anyways.

Audiofn

Hear is my opinion on adding weight to the bow. I did not say it earlier because I do not want to alarm you. More weight in the bow means more force when it drops from a landing. This increases your chance of a bow stear since you are going fast, so I do not like that option. How fast do you think/know you are going?

Jon

Iggy

Here's what I'd do.
I know some people will disagree with my method but I look at it as a learning experience. I'm a bit more adventurous than most.
If you don't feel comfortable doing this, hire a professional to explore its capabilities.

1. Get rid of the extra balast.
2. If you have indicators for the trim tabs check to make sure they read "0" or neutral when parallel with the hull bottom. Same for the drive trim.
3. Have fuel tank filled to around half full.
4. Launch the boat where you have plenty of room to run without having to come off plane to quickly.
5. Run boat at planing speed where it doesn't porpoise then set tabs and drive to "0" or neutral trim.
6. Increase throttle until it starts to porpoise.

If it doesn't porpoise and you reach WOT, reduce throttle to about 3/4 and adjust drive tim up to see what happens. If you trim up the prop starts to slip and nothing else happens, you've got it. Try running back up to WOT at that setting.

7. Keep increasing speed without adjusting trim to see if you can drive out of it. If it gets worse stop adding throttle.
If it becomes violent reduce throttle.
8. Try adjusting drive trim to bring the bow down until it stops porpoising. Note position on indicator. Try increasing speed untill it porpoises or you reach WOT without trouble. Reduce speed to previous setting and reset tim to neutral.
9. Now try adjusting the tabs down until it stops porpoising and note tab position. Again, increase speed until it porpoises or you reach WOT.

If at any time the boat feels like it's getting out of control reduce throttle until you feel comfortable.

10 If all is ok and you're at WOT try raisng the drive trim a little at a time to see what happens. If you reach the point where the prop starts to slip. Stop and trim down till it stops slipping and note the position. Then try raising the tabs a little at at a time.

By now you should have a good idea of what the boat feels like and what it, and you, can do.
Good luck.

Rdegeo4140

ursus what you say may be true but the cast hasn't changed. The same people are moving around in the same possitions as before. also I squeezed a 100#'s in a 20# bag. (See photo}. Also Formula built this hull with this power standard and also twin 260's.
I was told 110 gal tank was used and moved forward. That took 200#'s forward.

Thanks Audiofn for your concern. I'm not a ramjet yet. I put lead tire weights in my water supply bottle. About 120#'s. When engine package first put in I had to move waterline up 3". Now sits a little better.

Finally Iggy. I will try what you suggest. Another has given similar recommendations. Experience is what I need. At WOT last year I came down hard after jumping an unusually large wake and broke my hand inside steering wheel. Was out of water, came down ass first.
With alpha drive I seemed to be able to trim out more and porpoise less. I really don't want to break drive. I can't get more than 3degrees on drive with 6 degrees of tab. But I didn't try it your way. Hopefully this weekend.
Thanks Everyone
Happy Captain Bob

mcollinstn

Nobody has mentioned anything about your X dimension. Is there a chance that your new engine/drive setup was installed in such a manner as to put the propshaft centerline "lower" than it was before? A lower drive is more prone to porpoising than a higher one. Please (with the boat out of the water) set the drive trim to put the cavitation plate parallel to the bottom of the hull. Take a yardstick and hold it on the hull bottom and measure the distance between the yard stick and the cavitation plate. Give us a report in the following:

bottom of plate ?? inches above/below (whichever it is) the bottom of the hull.

Next: the 242LS was available with a 365hp 454 for sure (I drove one to a speedo-indicated 62mph, course who knows how fast that really was). You have absolutely NO MORE weight than that setup.

Weight: remove all unneccessary weight. As was said earlier, move necessary weight forward if you wish, but do not add any.

Trim Tabs: Your boat should make best top speed with your trim tabs FULLY retracted, or UP. Begin with the tabs all the way UP and trim the drive all the way DOWN. The boat may take some more time than usual to plane, but it should plane anyhow.

TRIM: with tabs fully UP and trim fully DOWN, increase throttle to wide open gradually. Allow boat to stop accelerating and take mental note of the RPM. Add one second of positive trim. Allow the rpm to stabilize and let the boat take a set for at least 5 seconds. Repeat the one-second UP trim and allow the boat to settle for 5 seconds. Continue this until the boat is making good speed and you still feel in control. At any time that porpoising becomes a problem, slow down - there is an issue that needs dealt with here: your BOAT should not be porpoising madly.

Porpoising is more likely at a given trim setting at LOWER speeds, than it is at higher speeds. For example, my 311 will take no more than trim at #2 at speeds less than 30mph before porpoising begins. At 50 mph, trim can go to #4 before porpoising begins. At 60 mph, trim can go to 6... Best speed is 72 mph at trim 7 to 8 - no porpoising, carrying the bow nicely.


Measure the X dimension. I am suspect of it..

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mcollinstn

Had a chance to measure yet?

Rdegeo4140

Sorry Mcollinstn,
The boat is hopefully in the water for the season. But please note that no alterations were made or needed changing over to Bravo drive. I know cavitation plate is slightly below transom.
Although I didn't follow your instructions to the "T" I managed 5 points trim but had 3 degrees down on tabs to jet smoothly. With 80 gals fuel,
500#'s in passenger weight, she did 4400 rpm's, 58mph paddle wheel and 54mph gps.
You're correct, the porposing occurs at
lower speeds and decreases with increased speed. Again it appears a lack of experience. I'm still not sure I like it's performance in choppy water, speed up or slow down, trim in or out. It never seems correct. I have had her out of the water a couple of times. Scary!
Again, thanks for the feedback.

mcollinstn

Yeah, I was wondering, though, if a Bravo is the same dimension from the input height to the propshaft height. I don't know the answer.

I am used to cavitation plates being one to four inches ABOVE the plane of the hull, but I have seen a Bayliner runabout (last week) that had the plate almost an inch BELOW.

58 indicated is getting close to where you should be. I still think you will end up three or four mph more when you get it all figured out.

As far as rough water usage, your hull will probably like a little tabs and set the drives neutral or so. You will need some speed to keep the boat on top of the crests.

Remember, though, that it will not take water like a larger boat.

Audiofn

Man that drive is DEEP in the water!!!!!