CONTINUOUSWAVE

Q1: can the acceleration onto plane of a 2012 170 DAUNTLESS with a 2012 Mercury 90 FourStroke be improved if the propeller is changed to a Mercury TROPHYplus four-bladed 17-pitch instead of a the present propeller, a Mercury LASER II three-bladed 19-pitch?

Q2: what other propeller change could improve acceleration onto plane when towing tubes or wakeboards?

BACKSTORY
I recently purchased a 2012 Dauntless 170 with the original Laser II 3 blade 19 pitch propeller and original 2012 Mercury four stroke. The engine already has a foil appendage extending the Anti-Ventilation plate aft. When pulling tubes or wakeboards the boat has trouble getting onto plane. The maximum rated horsepower is 90-HP.

I would like to try a four-blade Mercury TROPHYplus 17 pitch propeller to try to help the boat accelerate onto plane when pulling tubes or wakeboards.

I suspect you may never achieve the performance want from your 17 with a 90 HP four stroke engine. A 115 HP engine would be more appropriate for your boat. A four blade propeller of the right design should be very helpful. Removing the hydrofoil and ensuring the engine is mounted at the optimum height should also help performance. Proper engine trim will always provide better performance. The Trophy propeller you mention is a good candidate. If your local propeller dealer will allow you to try one out take advantage of the opportunity.

Reducing propeller pitch to 17 from 19 will improve the boat's performance accelerating onto plane when under greater loading. But working in the opposing direction, increasing to four-blades from three-blades will tend to increase the propeller load on the engine from the additional blade.

If you can obtain the TROPHYplus propeller on a trial-basis, it would be worth testing it, before you invest probably $500 or more in buying it.

Jefecinco--I [acknowledge] all your mentioned about the performance characteristics with a 90-HP engine on a 2012 170 DAUNTLESS.

Unfortunately the maximum engine power on [the mandatory U.S. Coast Guard capacity placard] is 90-HP.

I never thought about the hydrofoil being an [cause of reduced performance]. Is [the basis for thinking that an anti-ventilation plate foil appendage reduces performance because the foil] is causing too much drag?

I have purchased a used TROPHYplus four-bladed 17-pitch propeller. In the future I will report boat performance with that propeller.

jimh--I am also concerned that using a four-bladed propeller will add drag of the 4th blade. I guess I'll find out in a couple weeks when the propeller arrives. I will go out in a week to get some baseline numbers on time to plane. Thank you for the insight.

jaspermc wrote:jimh--I am also concerned that using a four-bladed propeller will add drag of the fourth blade.

The "drag" of the propeller is only present when the propeller is not rotating and some other propulsion method is moving the boat. What my comment was referencing is when switching to a four-blade propeller from a three-blade, there typically will be an increase in the total blade area of the propeller. The greater blade area makes the propeller have a higher load on the engine to turn the propeller as the propeller is trying to move more water with each revolution.

The result is that if you change, as you propose, from a three-blade 19-pich to a four-blade 17-pitch, you may find the engine speed will not increase as much as expected from the pitch change. The greater blade area of the four-blade will tend to add to the load on the engine, while the pitch change is tending to decrease the load. Exactly what the outcome will be in terms of what engine speed at full-throttle will result is best determined from actual testing.

I think you are correct in your instinct to go to a 4-blade prop, and the Trophy Plus 17" might be a good choice. But the Spitfire x7 in 15" pitch might be an even better one. It is always difficult to compare (or predict) propeller performance based on different boats and engines, but read my TrophyPlus/Spitfire experience on my 160 Dauntless at https://continuouswave.com/forum/viewtopic.php?t=7176.

The 160 Dauntless is a different (and heavier) boat, and with 115 HP rather than 90, but I based my decision on the published performance data for a 160 Super Sport with 90 HP. Your 170 Dauntless (which is more Montauk-like and not the heavier dual-console 170 Dauntless from the late 1990s) probably falls right between the 160 Super Sport and 160 Dauntless in weight. That would leave me concerned that the 17" TrophyPlus could be too much prop.

When I changed from a three-bladed stainless steel propeller to a four-bladed Stiletto (no longer manufactured) on our DAUNTLESS 16, a huge improvement in performance occurred. The improvements were vastly faster [acceleration from low speeds] and the ability to remain on plane at lower speeds. When the weather becomes snotty and you want to get back to the ramp quickly that attribute allows a higher speed without a terribly uncomfortable ride.

There was a minor loss of top speed at WOT. That was unimportant to me as I very seldom operated the boat at WOT except to avoid storms.

I also raised the engine mounting height and got rid of a hydrofoil when changing the propeller.