Raised motor, lost performance. Help Please.

[SnookHunter]

Hi, I'm new here and saw what a great place this was and have come to you for some help.

I have a 2005 16' lowe sea nymph utility boat with a 2005 Yamaha 4 stroke. I just put a jack plate on and now the anti-cavitation plate is even with the bottom of the boat and is set 5 inches back from the boat. Its a Bobs machine shop manual jack plate mini. And for some reason I have lost performance. Before the jack plate with my gps on a good day I could run 27.5 mph. Now I'm barely making 26mph. I put the jack plate on because I didnt like the the way the motor sprayed water up the back side of the engine and was told it would help performance. Since, the jack plate though the pitch of the motor has completely changed and now it sounds like the motor isnt lugging anymore. I still have the stock 9 7/8 x 10 1/2 prop. Is there something I'm doing wrong or something that can be adjusted to at least get back to where performance was at?

 

[bossee]

Re: Raised motor, lost performance. Help Please.

Hi,

How many hp on your 2005 Yamaha 4-stroke?

What is motor RPM on tachometer at full trottle now?

Can You raise the outboard one or two pin so the lower unit will make less drag in water (but risk propeller will suck air, at least in turns)?

How is the outboard trimmed now comparad to before?
Are you able to trim it out enough so the boat goes as easy as possible on the water at full throttle (and on plane)?

/Bo

 

[SnookHunter]

Re: Raised motor, lost performance. Help Please.

Its a 25hp yamaha tiller. I have another inch to play with and can raise it if needed. I couldnt tell ya the rpms since I dont have a tachometer. But the sound of the engine is definately louder and seems to work effortlessly.

The boat planes out no problem. And I can cruise at 21mph at a hair under half throttle, where as before it took over half but the top speed was higher. Also when I hit 27.5mph the motor was tucked under as far as it would go and the anti-cavitation plate was almost 2 inches below the boat. Now I have less drag and am slower. What gives? I should also mention that I have the same size prop as the stock one, but its made by Michigan wheel. My friend accidentally dropped my original one and it left a nice big nick in it, so I bought this one. Does that matter?