Rev4 Question

[scott diego]

So I had a mercury mirage plus 18p and just got a rev4 17p. (I have a 2320 with an F250)

I just put it on the same hub from the mirage. I am confirming they are interchangeable right? (It snugged up with the prop wrench)

There are 4 dime-size holes with plastic covers on the base of the rev4. I am supposed to leave all those closed right?

 

[grouperjim]

Yes, to the hub being the same.

I have experimented with all the different sized holes in the vent plugs. The solid plugs the prop comes with are fine. For the 2320/f250 I didn't find any noticeable performance advantage to venting the the prop.

 

[Reelysalty]

The holes allow for prop slip, more RPM to help
heavy boats get on plane....somewhat like
auto's torque converter.

Be sure to take advantage of Rev 4's excellent bite and
raise motor on bracket as the real use of a Rev 4 is
to reduce LU surface area in water.

 

[scott diego]

raise motor on bracket as the real use of a Rev 4 is
to reduce LU surface area in water.

I may be a little slow on this comment, what is "LU surface area"? (I am guessing Lower Unit? What doe you mean here?)

I also have a permatrim on my boat (which was an awesome addition, thanks again Grouperjim for the great advice), so I am thinking about raising it one hole. However, I dont want to go too crazy as I usually run my boat with 4 guys and start the dive/fish days with 150 gallons of fuel and a full bait tank. My concern is that if I raise it too much and I run the boat alone with little fuel it will be too high out of the water on plane...

 

[grouperjim]

My concern is that if I raise it too much and I run the boat alone with little fuel it will be too high out of the water on plane...

My thoughts on this issue differ from the owner/moderator of this site. A Parker is a fishing boat not a racing/performance machine. IMO a fishing boat should be setup with a priority for optimum handling rather than setting it up with a major concern to reduce friction for maximum top end speed/performance.

My experiences (engine setback on a bracket/DV hull) with both a 23DVCC and 2320 PH is that raising the motor to achieve optimum fuel efficiency and increased top end speed, for me, resulted in a negative which was that in certain following seas the prop broke loose/ventilated heavily even with the engine trimmed properly. Lowering the engine back down (factory setting) eliminated the ventilation issue.

My advice is that it is very easy to move the engine up or down meaning you should raise/adjust/run the engine in the highest position until you experience a negative such as ventilation.......then move it back down one hole. The affects of running the engine higher will differ between Mod v and deep v hulls as well as bracketed and notched transoms. The results will also vary in identical Parker models depending on your center of gravity and how you load the boat.

My 2320 ran level in the water as I set up my hull to run with weight forward. In addition to coolers etc. I carried over 100# of ground tackle in the anchor locker.........consequently the transom of my hull relatively speaking sat higher in the water than a hull with weight to the rear. This afforded me the ability to run on plane at slower speeds/improve ride quality in heavy chop. So, given variances in CG/loading of the hull etc. you can see how handling may be different in like hulls.

FWIW I also experimented with raising a 2520/f250 16 degree MV (Rev4). The 25MV went up a couple of holes before experiencing any following sea ventilation. These tests were done in the Gulf of Mexico where we often get short interval 2-4 chop.

YMMV

 

[Reelysalty]

I may be a little slow on this comment, what is "LU surface area"? (I am guessing Lower Unit? What doe you mean here?)

I also have a permatrim on my boat (which was an awesome addition, thanks again Grouperjim for the great advice), so I am thinking about raising it one hole. ..

LU is lower unit, if you don't want to raise your motor,
don't waste money on a Rev 4.

I see you're using a permatrim...sounds like your
boat might be underpowered for your use/conditions.

 

[soohoo]

I installed new rav 4's on my 2510 , the cavitation plate is even with the water at plane . With the rav 4's are you suggesting that it should be slightly higher because of the grip of that style prop ? I am getting 2mpg fully loaded , just wondering if I raise it one hole I might get a little better gas milage
Thanks Derek

 

[grouperjim]

The A/V plate is a control surface. It is the only control surface that enables you to raise the bow while tabs do the opposite.

That said, Rev 4 or any other prop I would raise the motor a hole at a time then run the boat and note any changes in how she handles/performs. As the A/V plate and prop get higher on the transom you will eventually experience a negative such as ventilation in certain seas or you may not be able to use the motor to trim the bow up as effectively as you were able to with the engine in a lower hole. Drop the motor back down one hole and that's your best set-up. Sometimes better fuel efficiency can come at the expense of better handling. YMMV

FWIW Permatrims/A/V plate add-on devices on bracketed boats are all about improving handling by adding additional hull planing surface area that is lost due to engine setback. Nothing to do with horsepower.

 

[shawnee83]

So I had a mercury mirage plus 18p and just got a rev4 17p. (I have a 2320 with an F250)



Do you still have the Mirage Plus 18P? What issues did you have with it? I've been thinking about trying it. Let me know if you sell it. FYI - I just installed the Permatrim a few weeks ago and I agree it's been a great addition. I also raised the motor all the way up. My cav plate and Permatrim are still a little under the water flow. This is not much help to you though as my 2120 is a notch and you are on a bracket. GROUPERJIM is technically correct about how to go about it. I just took a leap of faith based on others with the 2120 and my gut feelings. Figured I could always go back down but if I was right I only had to do it once. Good luck with your set up.

 

[Reelysalty]

This might help "clear the air" about "fins" added on lower units.

Also note comments as to motor angles/trim tab relationships.

fternoon gentleman,

I am Thomas and I work with Tabman in the Client Services department at Bennett Marine. Tabman is out of the office today, so I guess I will just jump in with both feet here and try to answer your questions.

I believe Lookin' For A Fight was wondering if his vessel needed a hydrofoil even though it had a set of trim tabs installed. I would start out by saying no, since a hydrofoil cannot provide the same lift, list control and trim capabilities as a set of properly sized trim tabs.

Now, let me explain this statement. Hydrofoils generate lift, just like a wing does on a plane, because the high pressure generated over the top the foil and the low pressure under it. You can make it work harder by using the tilt/trim on the outdrive when you tuck it under for hole shot and lifting the stern. Of course, the outdrive tilt/trim wasn’t designed to be used in this fashion; since you are using the prop’s thrust to lift the stern vs. moving the vessel (wasted energy, less efficient, increased stress & wear). The outdrive tilt/trim was really designed to position the prop parallel to the water flow, because this is the most efficient setting. Any time the prop is run at an angle you are increasing slippage and wasting RPM’s. Outdrives and foils cannot correct for list and they both become increasingly ineffective at lower speeds. When you use trim tabs to achieve the optimum running attitude of your vessel it relieves the prop/outdrive/hydrofoil of this burden and increases efficiency over a greater range of sea and loading conditions. Also, a hydrofoil cause’s drag all the time, since you cannot turn them off if you need them or not! They are just there stealing efficiency, wasting energy, and adding unneeded stress to your transom; where as trim tabs can be used or turned off until the next time! Something to think about!

Well, I guess I have spoken my piece on hydrofoils and can get down off my soap box now! /infopop/emoticons/icon_wink.gif I hope this has helped everyone to better understand how trim tabs work vs. foils. Of course, this explanation may have brought up some more questions for everyone and I will be very happy to answer them to best of my abilities, so just get back to me when you get chance.

I look forward to replies!

Happy Holidays,
MJ Thomas
Bennett Marine, Inc.
Client Services