Mercury V8 300HP prop?

Trout74

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Brand new 2021 Bennington 25LSAPG, with ESP. Boat weights 2800pds without engine. I’ll regularly carry 6-10 people. 4 of those will be children. Dealer has a 21 vengeance on it now. I think that’s too big. What prop? I’m thinking 14.5/17 Enertia.
thiughts? Thanks
 

Potomacbassin’

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I don't think you can go wrong with a 17 Enertia as a starting point. These boats are heavy so anything over 20p would require a very large amount of HP to get to 6000. Datalog your results (record MPH, MPG and GPH at 500 rpm increments) and compare against other users and performance bulletins. If testing by yourself you'll want to definitely be on the upper end of RPM range of the motor since you state you'll have 6-10 people aboard - I lose about 300-500rpm with 8 people aboard. Even better to test with load.

That V8 shouldn't have a problem pushing a 17 - I would be surprised if you needed a 16 with the Enertia. Yamaha SWS 16 is probably a good all-around prop with your expected load.

Consider raising the motor at least 1 hole with the Enertia - I found with the smaller diameter you are less likely to ventilate and can take advantage of some efficiency.
 

Trout74

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I don't think you can go wrong with a 17 Enertia as a starting point. These boats are heavy so anything over 20p would require a very large amount of HP to get to 6000. Datalog your results (record MPH, MPG and GPH at 500 rpm increments) and compare against other users and performance bulletins. If testing by yourself you'll want to definitely be on the upper end of RPM range of the motor since you state you'll have 6-10 people aboard - I lose about 300-500rpm with 8 people aboard. Even better to test with load.

That V8 shouldn't have a problem pushing a 17 - I would be surprised if you needed a 16 with the Enertia. Yamaha SWS 16 is probably a good all-around prop with your expected load.

Consider raising the motor at least 1 hole with the Enertia - I found with the smaller diameter you are less likely to ventilate and can take advantage of some efficiency.
Great information, thank you! Until it comes in, its back ordered, the dealer has a Mercury Vengnece 21 on it. I think that is big, but its no big deal to swap out props, he is on the water. Maybe the Vengence will be good, as long asI get the proper RPM, I don’t know if a enertia or Vengence or mirage make all that much difference. Could be wrong though.
 

Potomacbassin’

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I just saw the Vengeance 21 is a sub-14" diameter. Holy crap that may be a DOG down low with as much HP and weight you have. I don't have any personal experience but a lot of the internet forums talk about it being a very old and inefficient design.

Dealers are having a hard time sourcing props so it doesn't surprise me they're throwing on what is laying around, but I would be very surprised if you were happy with hole shot or fuel efficiency. Top speed might be ok but it'll take a while to get there. But like you said - at least you're on the water!

I would like to try a Mirage Plus one day to get my stern lifted a little more to see how it rides. I have a 16p SWSII on order as a spare and will test that this spring as well.

Congrats on the boat!
 

Vikingstaff

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The Enertia’s are a phenomenal performance minded Mercury prop. They pair great with the Merc’s.

I’d honestly start with an Enertia since you have a 300HP Mercury with your boat. I concur with going with the 17p version of it. With your motor that prop should be good with hole shot, but still deliver very good top end speed too.
 

The Hillbilly Barge

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My engine is two holes up, I have a 14.25 18p now, it does 47mph @5500 rpm, that's about 12% slippage, which is at the top of what's acceptable, two people full load of fuel, I feel the excessive slippage is due to the diameter of the prop.
 

Potomacbassin’

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I think the diameter may be to small, when looking at factory rigged boats, mercury puts 15.5x17p props constantly on their 300hp engines
Normally I would agree but with the Enertia it has an interesting design where the ears/blades are more swept back. I think this geometry allows it to keep a large enough blade area to minimize slip but also maintain a smaller diameter for more top speed.

In my own testing this proved to be true - the Enertia had a little more slip below 4000rpm versus a 15.25 SWSII prop, but I was able to get another 5mph on the top end. Props are all about tradeoffs and for me at least, the Enertia has more than adequate bite and efficiency down low but much more top speed. For others that may not be the objective, but I think everyone owes it to themselves to test a few props if they can afford it. Especially if they are going to put many hundreds of hours on their boat!
 
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