1986 REVENGE 21 Yamaha VF175 VMax SHO

Optimizing the performance of Boston Whaler boats
Dgoldfarb1957
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1986 REVENGE 21 Yamaha VF175 VMax SHO

Postby Dgoldfarb1957 » Tue Feb 02, 2021 10:19 pm

My son has a 1986 21-foot REVENGE. He is going to install a Yamaha VF175 V-MAX SHO engine to replace a Johnson V6 200-HP two-stroke-power-cycle engine.

What is an acceptable propeller for this boat and engine combination?


ASIDE: I just registered to participate in the forum. I want to find participants with experience with new Yamaha outboard engines.

jimh
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Re: 1986 REVENGE 21 Yamaha VF175 VMax SHO

Postby jimh » Wed Feb 03, 2021 9:59 am

In 1986 I do not believe Boston Whaler made a REVENGE 21 model. In 1986 Boston Whaler made the REVENGE Walk-Through in 20-, 22- and 25-foot lengths.

Earlier Boston Whaler made a REVENGE 21 model, but I believe production ended in 1982.

The designator REVENGE generally means the boat has a foredeck, a full-width windshield, and a helm station on starboard.

The REVENGE 21 boats did not really have a cabin under the foredeck--unless you viewed it from the perspective of a very small person. The REVENGE 21 boats used a hull with a rounded bottom at the stern. The windshield opened to permit access to the foredeck.

The REVENGE 22 boats were built on the OUTRAGE V-hull, and did not have the opening center portion of the windshield. They have an ample cuddy cabin.

The REVENGE Walk-Through boats were built on the OUTRAGE V-hull and had an opening center section of the windshield with a ladder to reach the foredeck. They were made in 20, 22, and 25-foot models. They had ample cuddy cabins.

To offer advice about a propeller for a particular boat and engine combination, readers will need to more about the boat you are referring to as a 1986 REVENGE 21. For some illustrations of different models called REVENGE, see my CETACEA Page 46 article at

Whose Revenge Is It?
http://continuouswave.com/whaler/cetacea/cetaceaPage46.html

Perhaps you can establish the actual model of your son's boat from the REVENGE models illustrated in CETACEA Page 46.

jimh
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Re: 1986 REVENGE 21 Yamaha VF175 VMax SHO

Postby jimh » Wed Feb 03, 2021 10:43 am

Do you have any data about the maximum boat speed that could be obtained with the previous 200-HP engine?

Generally boat speed at maximum power is related to the square-root of the the power-to-weight ratio. If the power decreases to 175-HP from 200-HP, then the boat speed would tend to decrease in proportion to (175/200)^0.5 or by a factor of 0.935, assuming the total weight of the boat did not change. For example, if the boat could reach 40-MPH with the 200-HP engine, the expected speed with 175-HP would be 40 x 0.935 = 37.4-MPH.

With this as the target speed, the propeller pitch would be selected so that at the maximum recommended crankshaft speed of the 175-HP engine, the boat speed would be 37.4-MPH. The engine gear ratio must also be known and included as a factor. The propeller SLIP can be estimated at 10-percent. A propeller calculator can then predict a PITCH value.

Yamaha-brand propellers are generally good propellers and will be a good fit for a Yamaha engine. Propellers from an engine OEM usually are more expensive than aftermarket brands.

If you provide the following information, a propeller pitch can be estimated:

  • prior top boat speed at full-throttle with 200-HP engine
  • weights of new and old engines
  • maximum engine speed recommended for new engine
  • gear ratio of new engine

I anticipate that a 17-pitch propeller may be a workable starting point.

Often with the sale of a new, loose engine for re-powering a boat, the selling dealer will provide the engine buyer with advice on propeller selection, and often provide test propellers to verify the choice. Dealers with experience as seller of a particular engine brand and that brand's particular engine models usually have experience in how those engines will perform on boats of a particular hull design and weight.

Dgoldfarb1957
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Re: 1986 REVENGE 21 Yamaha VF175 VMax SHO

Postby Dgoldfarb1957 » Fri Feb 05, 2021 3:31 pm

Thank you for your reply. The year of the revenge is earlier than 86. I just sent an inquiry to my son. Thank you for the information. The new outboard arrives today and hopefully the PDI by Yamaha will be performed next week. I’ve been told that the dealer can provide a propeller to test out to make to be able to ascertain the proper pitch and that the RPM’s are at the high range during WOT.