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New Boat Same Problem....Prop?

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X96mnn

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Bought a new boat, 2018 Avalon 1880 Bow Fisher, 25” pontoons with a Mercury 50HP command thrust engine that won’t turn over 4200 rpm. Unlike the boat before stuck at 3500 rpm it does not feel bogged down or come out of it for periods. I am thinking it is the prop, running a 4 blade, 13.8x13 currently, should I go to a 14x9 3 blade?
 
Running at 1000 and 2000 rpm is fine as long as the motor is not lugging at that speed. If it is, with high throttle settings, the motor will be damaged.

Jeff
 
New prop is on, it is with out any doubt a prop issue. Not sure if I have the right fit yet as it moves along the same at 6000 rpm but if I push the throttle more it goes above 6000, not sure how far past as I did not want to push it but I am thinking based on throttle position it would hit 6600RPM.
 
I am going to mention, even though the boat is just over a year old the dealer, even though they sold it new and propped it originally, plus made money when I bought it from them is not offering to cut me any breaks on new props. I payed $200 for this prop which is $20 less than their regular price. if I prop again I will be paying the full price for a new prop. I am thinking a 14 X 13 would hit the spot nice.

Motor an boat is still under warranty. They may be different if I was willing to take it back to them but it is a $140 in fuel round trip and roughly 8hrs of driving return. I did get a great deal, about 45% off of new so I have some money to play with.
 
Sounds like the dealer messed up with their prop calculations, or your hauling larger loads than they calculated for. Check up on prop calculation tables or just call Mercury Support. 920 929 5200 or 920 929 5040.
 
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It is not a larger load issue, boat is stock and just me in it for the test runs. Have used the prop calculator and the prop that came on it is one of the recommendations along with the prop I just put on is there as well.

Not sure if it is fair to say the dealer messed up, I like to think they did but in all fairness it may have been setup for the person who originally bought the boat. The original 13.8 X 13 prop works well, great acceleration, top speed of 18mph and a cruse speed of 5mph at 1800 rpm makes for a cheap day. Had the engine checked by a boat mechanic, (Not Mercury) and he stated there was no lugging of the motor, he actually thought the rpm gauge my be off a little but we confirmed it was not.

Guess what I need to decide is, do I want a boat that is better equipped for 90% of my running and lacking for 10% of my running compared to vise versa. I will cruise for 4hrs following the coast line at 5 to 7 mph, at sunset cook it home before dark. Going with a 14 X 13 three blade may literally buy me an extra 10 minutes of cruise before turning around per trip. It will cost me a lot more gas as cruise speed will be at 3000 rpm compared to 1800rpm with three blade plus another couple hundred dollars.

Think I will give Mercury a call. Thanks for the numbers.
 
So this boat and engine apparently can defy all points of logic.

Quick recap, 18ft 2200 pd pontoon boat with 50hp mercury command thrust.
Original prop was a 4 blade 14x13 and hit 4000 rpm with just me and 3800 with the family. 18mph with just me and 15 with the family.
Second prop was 3 blade 14x9 and hit 6600 rpm and 19.5 mph wth just me and 17mph with the family.
Third prop is a 3 blade 14x13 and hits 4400 rpm and 17mph with family, never tested with just me.

Losing 2100 rpm on a 4 pitch change not impossible? I thought max loss would be 600rpm. Any ideas?
 
Your working with a lot of weight and even 4 stroke outboards are a "peaky" power profile. Proper rpm means both efficiency and power.
 
timguy said:
Your working with a lot of weight and even 4 stroke outboards are a "peaky" power profile. Proper rpm means both efficiency and power.
Click to expand...

This is what I am thinking as well. The motor sounds great and there is no lugging with the 14x13 4 or three blade, I get good speed and my low and slow rpm lets me go a long ways on a single tank of fuel.
 
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