1998 25 hp Merc 14’ Lowe V

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ktoelke54

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I’m sorting things out with this, new to me, boat and motor and had a couple questions. But first I’d like to say thanks to the person who posted a question about a hard starting 96 merc and those who replied. I was confusing the primer on this motor with a choke. Now that I have that straight, it starts much easier.

The problem I’m having is with prop blowout. It only happens if you give it full throttle before it’s up on plane. The cavitation plate is level with the bottom of the boat, maybe just a little above. The motor is setting all the way down on the transom.

It has a thirteen pitch three blade, standard for this motor. It tops out at about 25 mph with a load. I’d guess about the middle of it’s power band.

I was thinking a four blade 12 might get me out of the hole better and hopefully not loose much on the top? I’d like to eliminate as much of the blowout as possible without loosing too much speed, looking for ideas?



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1st step would be to get an induction tach so you know what RPM's you're dealing with. A cupped edge might help with the blowout without having to swap props around. I was having a similar issue with my motor (same motor, older year) on my 1436 and the cupped edge help stop the slip/blowout but was probably done too aggressively by the shop as it slowed the RPM's a great deal.
 
I've had several 14' boats and every one of them did something similar or had a hard time getting on plane, or cavitate while turning. Especially narrow boats or ones that had added weight such as decks. Every one of those boats responded well to a hydrofoil. I'm a huge believer and have used both stingray and doel fin. Helps pop on plane super easy, no more prop blowout ever, allows to run a higher trim position without porpising. Some guys say they hurt top end speed, I never noticed by the seat of my pants but I sure did notice all the other differences!

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onthewater102 said:
1st step would be to get an induction tach so you know what RPM's you're dealing with. A cupped edge might help with the blowout without having to swap props around. I was having a similar issue with my motor (same motor, older year) on my 1436 and the cupped edge help stop the slip/blowout but was probably done too aggressively by the shop as it slowed the RPM's a great deal.

Checked it with a tach —. 5400


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Operating range per the manual for that motor is 5k-6k, so you're already below the middle of the range, going much lower is really loading up the motor.

When you switch from a 3 blade to a 4 blade most prop manufacturers recommend you drop 1" in pitch, however you should probably be dropping 1" in pitch sticking with the 3 blade as it stands to take some load off the motor - so if you're making the switch to a 4 blade you probably want to drop to an 11P.

Small motors vary a lot with changes in pitch, far more than the 200 rpm per inch of change that is typical of larger motors, so hopefully you have a shop where you can try a few things out on a test basis and return/exchange with them until you find a proper match to your hull/loads.
 

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