Bad Porpoise
 

I have a Hallett 270 with the 2 step hull, just added some more power and now at 80-90 mph it has a terrible porpoise problem.
I currently run a Bravo 30p 4 blade, would a 5 blade help ? I am also running a Imco Extreme drive with extender box....

anyone ???

That porpoise should just be the boat losing suction and then grabbing the water again I would think. Maybe the drive is too deep. If you go with a shorty then I would definetly put on a 5 blade. My Fountain gets squirrly at 80-90 but no bouncing at all. I would like to see some expert opinions.

I'm already running a fairly short Imco drive ...

Porpoising can be caused by a few things. The bottom configuration can be built with a rocker or a hook. These situations can be induced by the builder purposely or can be in the bottom due to storage or bad builds. Ultimately a boat will porpoise because the propeller is trying to caryy the bow higher and at some point is unable to do so due to drive height, CG or one of the first mentioned issues. Set up can amplify these results (drive height, set back, propeller selection). Also, some boats just weren't built or tested to run in the speeds we are trying to get them into.

Try a 5 blade propeller. It will lift the stern more and may cause the boat to run slightly flatter as it was intended to do. If this doesn't help, going the oposite way by building bow carrying help into the 4 blade prop is a great option. Ultimately drive heights may need to be adjusted. Lastly, talk to Hallet and see if they have this issue on the 270's with your set up.

Thanks Bblades, I did talk to Hallett, but they weren't as definitive as I would of liked.I too think I should try a 5 blade, but was looking for
a little more direction before I embark on the task of prop testing .

Put a long straight edge on the bottom running surfaces. A hook is the hollow above a straight edge. A hook will cause suction and hold the boat in the water. Generally bottoms going near a hundred or more are perfectly straight. No hooks or rockers. Some hulls usually conventional v's will have a slight rocker to help lift the bow. Others may have hooks near the outer strakes to help the boat run flat. Its possible a slight rocker was designed in to the boat increasing the speed with stock power and now you have passed that targeted speed. Just a guess see what you have and deal accordingly.

Was it hopping before you added the HP? Were you running in that speed range before? What is your red line? What R's were you hitting at WOT?

It didn't happen before because all I could obtain top speed was 80
The bottom appears straight but my slip numbers are a little high,

above 15%...now from 80 on up its hops unless the tabs are dragged
for a while...

I have a Lavey 2750 that had a bad porpoise problem over 70 mph. After I put a Whipple on it it really got exciting. I tried different props, 4 & 5 and no help. Finally had the bottom blueprinted and removed a couple lifting strakes and went with a 2" Imco shortie with a Hering 5 blade. Now I can run low 90's with no bounce at all, almost can run it hands off, and no tabs. Very happy but a little poorer.

Sounds fun....and sounds like a bravo eater with that whipple and 5 blade.

It is quite an improvement for sure- I fought it for 5 years and went back and forth with Lavey, who were no help at all- said it was driver, not the boat. Turns out it was the boat. Now it's fun, and we have gone by a few Bravo's, but there are sure alot more that will go by us. At least we're not bouncing when they do.

My 270 hallett only porpoises in flat to semi flat water. Before the engine upgrade it would porpoise around 68 to top speed of 75mph. I purchased a 5 blade Maximus and it helped a little but still porpoised in flat water (The five blade did carry the bow a little higher at higher speeds).

Talked to Hallet and received no useful info.

Since the upgraded HP (800hp and -2 IMCO drive) the boat still porpoises around 70 to 80 in flat water and goes away up to about 90mph. I currently have a stock 4 blade 32p prop with the engine upgrade and won't put on a 5 blade since the outdrive (XR) won't last with that much HP and bite from the prop.

I personally think the Hallet 270 is a heavy boat for it's size and to try and maintain the bow up at the higher speeds in smooth water is asking a lot from the prop (bow lift). I guess that is why the Hallet rides so smoooooooth in rough water. Take the good with the bad. I've have to admit the boat handles like a dream above 80 and besides the inconveince of the propoising in flat water it's very stable.... I do notice that the porpoising reduces with less trim which is expected since the prop is not trying to lift the bow as high.

Before I spent a ton of time and money on anything else try a little smaller diameter prop.

Hmmm...a five blade ? what pitch ? do you still have it ? what rpm did you turn it ? mph ?

I sold the five blade, I had a 4 blade 28 and purchased a five blade 26 before the big HP upgrade. They both turned about 5200 and the top spped was within 1 mph of each other (74 to 75). I noticed a better cruisng rpm with the five blade (minus 200 rpm's vs the four blade). However it really did not help much with the porpoise issue.

The 5 blase was labbed by Mercruiser which had the diameter turned down to about 15 1/4" from the stock diameter. My prop slip went down but I think the my XR gears paid a price for the five blade prop. I took the new drive apart to install the -2 lower unit and noticed some wear issues on the gears. I only had a couple of hours on the drive and most of them was with the five blade. I was always easy coming out of the hole and changed my drive oil every 10 hrs. The marine shop (GT marine) even gussed that I was running a five blade from looking at the gears when they were taking it apart. I never told them I had a five blade and the prop was already sold.

Hope this info helps....

zz

That's what I've heard, but my XZ drive seems to be holding up so far.

Hallett Fan: I have a new unlabbed 30 pitch Maximus. Ran it once for testing, but like VegasHallett I have been reluctant to put the wear on the XR gears.

Hot Lavey: Where did you get your bottom blueprinting done? I've considered this.

Gears wear. Shavings are normal. Chunks are not. Most wear occurs in the first few hours of usage.

5 blade propellers will not wreck a drive if used in the proper methods and with the proper HP ranges per the drives capabilities.

Extreme Custom Marine in Elsinore. Fantastic guys to work with and very fair on pricing.

I believe the XR is only rated for 600HP and putting a five blade on a XR drive with a motor over 600HP is asking for trouble. I realize you can still hurt a drive with a four blade but putting a five blade on will dramatically increase your chances of buying more parts for your drive.

As BBlades said "5 blade propellers will not wreck a drive "IF" the drive is rated properly. I love the five blade set up but not with over 725hp and a XR drive.:D

I have the Imco Extreme drive, it should be a little stronger than a stock Bravo XR...I'm fairly easy on it also, I don't like to abuse things,
especially if I have to pay for it ! At this point , I think my best bet is to try the 5 blade ..maybe the 30 pitch ?

If you normally run a 30p four blade you will need a 28p five blade. Also the Maximus has a larger diameter 15 5/8" out of the box and Mercruiser recommends turning the diameter down to 15' or 15 1/4" for certain performance boats.

Also the IMCO Extreme uses stock mercruiser XR parts (gears/shafts). Thier housings (upper/lower) are much stronger but the internal major parts are still the same.

Brett from BBLades can hook you up with everything you need regarding which five blade to run. He told me in the past he has put some five blades on Halletts and had some good advice.

I can turn the 30 Bravo to 6200 rpm...I'm thinking maybe a 30 p
Maximus might be the way to go ?