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Mercruiser outdrive cruising plane

J

John Cruiser

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I have a 28 foot10 foot beam FiberForm cruiser. It has twin engine. It has twin engine Merc cruiser 165 IO's. Can I use the cruise planes to help get it out of the water without damaging the outdrive or the stern. Please share experiences and opinions.
 
It has twin engine Merc cruiser 165 IO's. Can I use the cruise planes to help get it out of the water without damaging the outdrive or the stern.
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This boat is obviously an older model. Do you have the correct props on the ODs? Are you putting the ODs in the down position and trimming them to the optimum engine RPM for maximum thrust? If it won't readily plane then suspect the engines are tired and low on compression. Using the cruise planes will help some but the tired engines must be addressed. Are they straight 4 or 6 cylinder engines? Fresh powerplants will greatly improve performance.
 
I have the cruise planes and they work appropriately.The boat is actually quite fast with dual stainless steel props, reaching 30 miles an hour. What I'm referring to is the whale tail type of hydrofoil that bolts to the out drives that perhaps would keep me on a plane at a lower RPM then 3000-3300 RPMs. I hear the conflict that they are great and can lower your RPM which would be more efficient or that they are hard on your transom and/or your outdrive?
 
Yes you can use them, Should you use them? I say NO but it is not my boat.

What the "whale tails" do is interfere with steering control at higher speeds, They will help a under powered boat achieve plane quicker. But it typically sacrifices high speed. IE: it keeps the bow down as you want the bow and boat out of the water for max speed.

If you allready have trim tabs on each side of your boat you should not need the ones for the ANTICAVITAION plate on the outdrive. Are the trim tabs hydraulic or spring loaded?

Are they older ones? maybe a newer set that may be a bit larger would help plaining off quicker.

Have you tried a smaller pitch prop?
 
I believe the planes are the original 1976ones. The props on the engine's I think are correct because they will go to 4300 RPM + both sides at wide open throttle. Larger planes might do the trick.
 
Your objective was to get on plaine quicker. Not to reach max rpm at wide open throttle.

With that style/size boat and of that vintage with two inline six cylinders you have several limitations so you will have to sacrifice one FOR the other. Actually with your set up going to a smaller pitch prop would help, (if you are running 19 p go to 17p or 15p) of course use aluminium to test not stainless steel. With that boat I dont see you needing to run at wide open throttle so a loss of 5 MPH or so at top speed should not break the bank..

Your call but as Chief said you are EXACTLY where it should be ( at wide open throttle) under ideal conditions.

Maybe a 4 bladed prop would be effective???
 
Are we forgetting the golden rule. The motor must achieve the recommended wot . 4200-4600 rpm.

A 4 blade prop on each drive with put him around 3800 maybe less rpm.

Again leave it alone, or one or both of these motor are going to go they are old and when you start lugging them they will be giving up the ghost.
 
Chief,

That is the optimal set up for any boat, to achive max rpm at WOT.

But that rule also holds true for a more normal boat, say a 21 ft 350 i/o single engine ( WOT 4400-4600, 52+ mph, no isues comming out of the water)

To be a bit blunt here, He has a slug, a barge, an old timer boat that is big and heavy and underpowered. ( that boat should have twin V8's) He is fortunate that it appears to be set up propperly to achive max rpms.....BUT max rpms is not always a desired net result especially for a big boat as his is.

He would not want to run those motors at 4300 rpms for very long. They would be working very hard as I am sure they are!!

He is looking for better out of the hole performance and we are making suggestions.

As I said there is a sacrifice to be made, A better hole shot requires a smaller pitch prop or even a 4 blade, thus quicker acceration but loss of max MPH and a possible increase in max RPMS....

I would venture to say that he is willing to lose Max MPH for a better hole shot. Many boats use smaller pitch when towing skiiers. One just must understand the unintended results of this when running at higher speeds...

JMHO
 
Wouldn't he need only to lower the prop pitch to achieve the required RPM range? I agree; lugging old engines are not what one wants to do.
 
Thanks to all who replied to this thread. I will leave as is.most of the time we will cruise at displacement level. What would be the optimum rpm to run this straight 6 efficiently without carboning up the engine?
 
You will not carbon up those engines at almost any speed.... in my opinion......your cars/trucks do not do this......Also it appears your set up is tuned very well. The engine uses what it needs for fuel. If you have a rich condition then it would carbon up.

The bottom line from above conversations is to achieve a better hole shot a prop change ( pitch or qty of blades) would be reccommended. The addition of a whale tail is not reccommended.....
 
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