Baja Speed

[tryinlinux]

Hello all again,
I was wondering if anyone has an idea how fast a 1983 Baja 16SS should go with a Mariner 70HP outboard, and a 10-1/4"X14 pitch prop? I have clocked it with my GPS at only 33mph max! (there isn't a speedo in this boat) This seems to me to be a bit slow considering a boat I had years ago (a Baretta 16' trihull with a 55hp Evenrude would do approx 38mph) Any ideas, or is it on track for this boat.I would figure this very shallow v hull , and no open bow should also at least be pushing the 40 mph mark. This boat purchased recently had a new prop which looks too small for the engine on it. I am wondering if the owner just threw on a "cheapie" just to get rid of it. Any help is appreciated.
Thank you
Jim

 

[Cooperider]

Yes, it should go faster than that, try a bigger prop. You should be in the 40 range for speed. Beyond that you might need a bigger motor.

I'll see if I can find some pix for you.

 

[tryinlinux]

Thanks,
Today on the water today I clocked it at 33mph at 5500rpms, so I was thinking of going to a 10-1/4" prop with a 16 pitch ,...this will slow down the rpms a bit as well as increase my speed without lugging the engine. Does this sound about right, and how much of a speed increase do you think I could gain from this?

 

[Chris]

Jim,

You probably already know this, but you want to find a pitch that keeps your motor running in it's maximum RPM range at wide open throttle. You don't want to be over that range, nor under. Do you know the recommeded max RPM for your motor? Also, you might want to try a stainless steel prop assuming that's not what you're running. They're usually good for a few more MPH. As you go up in pitch, your RPM's will drop, as you go down in pitch they'll rise. So the trick is to find the one that keeps your motor in it's sweet spot.

Also, trim can make a big difference with top end. Do you have power-trim? Or is it just manual trim? If it's manual trim, you might want to try playing around with it a bit and see if you can find the set up that works best.

-Chris

 

[tryinlinux]

Thanks for the reply.
Yes I did know that info. My sweet spot is between 5300 and 5800 rpms max.I am right in the middle running my aluminum prop. I am thinking I can go up in pitch, decrease my rpms slightly, increase my speed slightly,...but how far can I go? What is the rule of thumb? ie: 1 degree in pitch will increase/decrease speed by how much? How much in each degree of pitch will increase/decrease speed?
Any info, or tips are appreciated!
Thanks
Jim (eager to go faster)

 

[Chris]

1 inch usually reduces or increases your RPM by about 200.

If you change to Stainless Steel, that will also change your RPM's a bit as well as the blades flex less than Aluminum.


-Chris

 

[tryinlinux]

Do you know what kind of a speed increase you can gain by upping the pitch by 1"?. Just trying to figure out if it's going to be worth doing if the increase is minimal.I don't want to "water a dead tree" if you know what I mean.
Thanks
Jim

 

[Chris]

Do you know what kind of a speed increase you can gain by upping the pitch by 1"?. Just trying to figure out if it's going to be worth doing if the increase is minimal.I don't want to "water a dead tree" if you know what I mean.
Thanks
Jim

Jim, it's really hard to predict.

I'm not sure if you ever said whether you have power-trim or not?

I ask as sometimes freeing a boat up will net better top end gains than a one inch difference in pitch. And also, you might find if you can break the boat loose from the water you'll run at higher RPM's as well.

-Chris