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  Any experience with a 4-blade prop on a 15' Sport or other Whaler?

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Author Topic:   Any experience with a 4-blade prop on a 15' Sport or other Whaler?
SuburbanBoy posted 03-02-2001 04:44 PM ET (US)   Profile for SuburbanBoy   Send Email to SuburbanBoy  
Any experience with a 4 Blade prop with a 15' Sport or other Whaler? I am in the process of a repower on my 15' Striper. In researching power plants I ran across the issue of props. I am willing to purchase two props, one for crusing, one for skiing. I worked with a Mercury Prop Engineer on this problem. While it is dangerous to generalize about any technical issue, one point he made over and over was the advantage of a 4-blade prop for my Whaler vs. the standard 3-blade. He said they are much smoother and will turn better, accelerate better and pull out a skiier better. He said I might sacrifice a very small amount of top speed. He painted a convincing picture of the value of a 4-blade prop. We were setting up the 60hp Merc 4cycle for my 15' Striper. Has anyone had any direct experience with a 4-blade prop? While this topic may have been covered in the past, this may a good time to revisit this topic as many forum members are going thru the spring setup ritual with their Whaler, and some will consider a prop replacement.


awares posted 03-02-2001 05:44 PM ET (US)     Profile for awares  Send Email to awares     
When I was fishing the bass tournament trail I always ran a 4 blade prop on my Ranger
bass boat.
The hole shot was quicker and my prop never slipped from wave to wave. I tried several
props and found a nice fit without loosing speed.
I liked them and I think they would great for some of the Whalers.
Clark Roberts posted 03-04-2001 10:34 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
The number of blades is only one aspect of a prop. Others are material, pitch, diameter, and type of blade. These choices are driven by the boat, engine and performance characteristics desired. I have run two, three, four and five blade props and in my opinion the 5 blade was smoothest,,, seems logical... etc, etc.. the two blades were the fastest and best all around performance with 3 blades... if power is the goal (for pulling, towing, offshore hanging on the back of a wave, etc.... then a 4 blade may be best choice! The more blades the better the grip at low rpm . Testing is the only way to be sure.... been there done that.. Happy Whalin'... Clark
jimh posted 03-04-2001 02:06 PM ET (US)     Profile for jimh  Send Email to jimh     
When the French launched their majestic NORMANDIE in the 1930's it was the biggest and fastest liner in the world. The rich and famous booked passage on her, but there was an annoying problem: vibration.

After her first season, she was refitted with new propellers and some additional stiffening was added to her hull. The props changed from 3-blade to 4-blade. The vibration was gone.

lhg posted 03-04-2001 03:53 PM ET (US)     Profile for lhg    
Unless one is using a 70/75 HP engine on a 15, I don't think 4 bladed props are available for the small gearcases used by the smaller engines. And I wouldn't think a "Bigfoot" (mid sized 4 1/4") gear case would be correct for a Merc 60 on a 15. So you may have a hard time finding a 4 blade for it.

I too have become aware that lately Mercury has been recommending 4 bladed props for most of their mid-range and up engines, so they must know something here. Their one stumble in this type was the original "Trophy" prop, which took HUGE amounts of power to spin, and required 3" of engine height to run properly. A prop strictly for the bass boaters. This prop was quickly redesigned into the Trophy Plus, which I hear is far superior, and more general purpose in use.

For the large gearcase models, they have also brought out a 4 blade Offshore model (aggressive holding offshore and great hull lift), a 4 blade Revolution for performance outboard applications, and 4 blade Bravo props for both outboard and stern drives (also go-fast). And finally a lower cost four bladed aluminium for slower, heavier, single and dual CR outboard/stern drive cruising applications. So these must be the props of choice nowadays, 75HP and up.

I am hearing that design technology is now allowing these newer 4 blades to be just about as fast as 3 blades, especially the Trophy Plus, Revolution and Bravo models.
They also have great mid range speed for a given RPM. If you're running 4000RPM and 35 mph with a 3 blade, you'll be doing close to 40 with a 4 blade at same RPM. Then, as you get to max RPM's, speed equals out again.

Remember, with any SS 4 blade, the engine should be lifted about 1 1/2" (2 bolt holes). If you're going to run them fully submerged, drop down 2" pitch as compared to your standard 3 blade "elephant ear" prop.

SuburbanBoy posted 03-04-2001 11:42 PM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
The Mercury Prop Engineer recommmended a Mercury 4blade propellor model "Trophy Sport" suitabe for engines from 30 to 60 hp, with a 12 - 15' pitch. He mentioned that it should fit the standard gear model of the 60 4cycle. An earlier post mentioned that the transom mounting hole pattern is the same for all current motors. This will help to allow for installation and height changes. Which brings me to another point that the Engineer made which was in reference to motor height. For skiing he suggested I drop the motor down to minimize any "rooster tail". For crusing he suggested I raise the motor to increase top speed. He stated several times that my 15' Striper was NOT a performance boat, and that I should be satisfied with a great skiing, fishing and cruising boat, and that I should leave the high-performance stuff to other boats. I was grateful for his suggestions and took it as a compliment.
lhg posted 03-04-2001 11:58 PM ET (US)     Profile for lhg    
Thanks for the info on yet another new Merc 4 bladed prop. Didn't know they were making one for the lower HP engines, but sounds good. I'd take their recommendation, as they REALLY know their stuff, obviously. Not raising the engine much makes some sense, as I know they don't recommend much height for speeds less than 40mph.

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