4 blade prop on a 20?

[DoozleD]

SO I have a 20 Master Angler, I was kicking around the idea of a 4blader? I have had good luck with them on my past boats, any thoughts/ideas/suggestions?...its a 115 Yamaha..

[Bushwacker]

Welcome to CSC! 4B props generally produce more stern lift, so would be particularly advantageous if you have a heavy 4 stroke motor, as it will allow the boat to hang on plane at a lower speed. The trade off is the drag of the extra blade, which will typically give you a lower top speed.

The 19/20' hulls were designed for the largest outboards available in the mid 60's, which weighed no more than about 300 lbs! The VDH hull is very stiff but relatively light and very efficient, so does not need nearly as much power as a typical modern Deep V. Many were sold new in the 60's and 70's with 85-100 hp motors. With a 300 lb motor. they will plane at about 12 mph without trim tabs and a 3B prop. A 115 should give you WOT speeds in the low-mid-30's, maybe even high 30's with a very light load. It's hard to find a modern motor that light today. although 3 and 4 cylinder 2 strokes will come close.

If you have a 2-stroke motor, it may be light enough that you might get a better combination of WOT speed, low planing speed and good fuel economy with a 3B prop. I'm not familiar with the Yamaha props, but the Merc Mirage series and BRP Rebel 3B props have large blades and a good reputation for good low speed planing and fuel economy. If you have a 400 lb + 4 stroke, a 4B prop will probably provide a lower planing speed and good cruise fuel economy but a bit lower WOT speed.

Before you start changing props, make sure your tach is accurate. (analog tachs are notoriously inaccurate, but the digital tachs that connect to the engine computer on the newer motors are very accurate.) Also make sure the top of the Anti Ventilation plate is above green water when you're up on plane and fully trimmed out. When motor height is right, the AV plate is typically 1-2" above bottom of hull; most dealers seem to mount them too low. Prop trials should be run with the heaviest load you normally run and WOT should be near the top of the recommended rpm range for the motor.

[McGillicuddy]

What Bushwacker said, minus the Mirage. I can't speak to the Rebel Blades. I don't think the Merc Mirage is appropriate or even available in that size.

In a 4 blade, try a Merc Alpha 4 or the Solas version, Amita 4 - I think, if you're fine with aluminum. These props are very similar to the time tested merc black max.

If you want stainless, check PowerTech's SCD 4 which is a 4 blade version of Yamahas semi cleaver (also a very good design for your combo), or the MQF4 which is a 4 blade version of Mercurys Black Max geometry. Size will be roughly 13.5 x 15p or 13.25 x 17p. Great stern-lift and handling and lower plane speed from all. Hole-shot will also be very good. 3 blade variants in each of those props are also available. Each of those should get you 34-37 mph. Maybe more with the 3 blade stainless options.

The 4stroke is about 400 lbs & the 2 stroke closer to 350. What prop are you running now on what model motor. I think the merc black max is just perfect for a 115 on a 20 SeaCraft, but the MQF or SCD stainless props can't help but improve performance. Splitting hairs? Maybe. About $200 difference for SS 3 blades. More for 4 blades If you have a 4 stroke I would expect better lift from the Merc design or the MQF from PowerTech props.

[DoozleD]

thanks guys!

[FishStretcher]

I am happy with a Solas amita 4 in 13.25 x 15P. I have a yamaha F100. Especially at $90. The F115 has a different lower unit ratio so it works well for it too. The boat just goes faster. Get a planing fin (doel fin or sting ray or hydro shield), too.

[DoozleD]

i was running a Solas 4-plader on my Scarab, and I was extremely happy with it! ran allot smother, allot more stern lift , and was just over all great, I didn't notice allot of loss in the top end..so im not really that worried about the loss of top speed on my seacraft