need help on prop for a 21 sea hawk 09

cloudbusterb · 06-08-2009, 03:45 PM

I am running a 225 yamaha and need help on the right prop size. My boat only will turn 5000 rpms at 42 mph i need it to run up to the 6000 rpms.

Starfish · 06-08-2009, 05:01 PM

It might help to know what prop you currently are running. Also whether you're running an offshore bracket and how high the engine is mounted.

cloudbusterb · 06-08-2009, 08:30 PM

the prop is a 21t-15 i get 4100rpm at 41mph the other is a 19t-15 1/4 rpm 5100 at 41 mph i never trimed the engine up i left it down all the way . the engine is mounted on the first hole which puts it down in the water all the way . I had y marine do it in coose bay thought they know whats going on. I only have 5 hours on the engine so i am still breaking it in. I can email pics of the set up on the off shore bracket the kicker sits very low in the water also.Is yours like that

packer · 06-08-2009, 08:40 PM

The 6000rpm is the max recomended rpm ,which you should be able to get close to with a light load and play with the trim to get max speed . If you prop your boat for 6000rpm loaded you will probably easily overspeed it when loaded light . the 19 pitch should work good when your engine is broken in and you have learned to ply with the trim . You can easily pick up 500rpm by trimming the boat out

cloudbusterb · 06-08-2009, 08:50 PM

Thanks packer i had 70 gals of fuel and 6 adults in the boat and 2 kids and i dont know how to trim the boat out verry good yet Im a pilot not a boater yet but will learn. only drove it 2 times so far. I have some pics of how the engine was mounted and was concered it is too low in the water

Starfish · 06-09-2009, 03:17 AM

Definitely you'll want to adjust your trim before reaching any conclusions about your props. You should start out with the motor trimmed down, give it throttle until you're up on plane, then trim it up until you feel the front end of the boat lighten up and you'll see the splash line move from the front of the boat toward the rear. Keep trimming until you start porpoising and then back off the trim and trim back down a little until it just stops porpoising. On most boats you'll find that the more throttle you are running the more it can be trimmed up, i.e. at full throttle you might be at full trim. You'll likely find a huge difference in top speed and RPM compared to running at full down trim.

Seems like most boat shops set up the engines too low in the water. Your cavitation plate should be a little above the bottom of the boat for optimum performance on most boats, but there's really no way to tell for sure except to adjust it and see.

Mooch · 06-09-2009, 06:12 AM

Quote:

Originally Posted by Starfish

Seems like most boat shops set up the engines too low in the water. Your cavitation plate should be a little above the bottom of the boat for optimum performance on most boats, but there's really no way to tell for sure except to adjust it and see.

I've yet to see a Seahawk with the engine mounted anywhere but as low as it will go. Dealers are lazy and the faster they can get them rigged the more money they make.

I had to raise the F150 on my Seahawk a couple holes from where it was rigged at North River. I picked up a couple hundred rpm just by raising it. Not to mention it handled better,and burns less fuel also.

Definately learn to use your trim. Like was mention,a 500 rpm increase with a trimmed out engine is entirely possible.

cloudbusterb · 06-09-2009, 07:49 AM

You guys are great thanks for all your help i was so dissipointed in my sea trials that i didnt know if i got ripped off or what on my set up. How did you break you new engins in .

cloudbusterb · 06-09-2009, 07:51 AM

this time i will go out by my self and warm the boat up then try to get some readings with the trim up . fuel will be arond 55 gals.

Schenley · 06-09-2009, 08:04 AM

Quote:

Originally Posted by cloudbusterb

this time i will go out by my self and warm the boat up then try to get some readings with the trim up . fuel will be arond 55 gals.

Since you do seem to be a "bit short on experience" I would strongly suggest that you get a knowledable boater to accompany you until you can feel confident in your, and the boats abilities.

Magnum · 06-09-2009, 08:38 AM

Quote:

Originally Posted by cloudbusterb

How did you break you new engins in .

Pull your Yamaha users manual out of your glove box & read the break in instructions section. It will tell you all you need to know.

Mooch · 06-09-2009, 10:55 AM

Quote:

Originally Posted by Magnum

Pull your Yamaha users manual out of your glove box & read the break in instructions section. It will tell you all you need to know.

When you're done with the break-in,make sure and run the engines hard. 4 strokes don't like to be babied. You don't need to run around at wide open throttle all the time,but high rpm for a few minutes every trip is good for them.

You need to be sure they get good and hot so they'll burn off any moisture or fuel in the crankcase. The water in the NW is cold. Running low rpm in cold water is like making tons of short trips without getting your car up to operating temps.

cloudbusterb · 06-09-2009, 03:32 PM

I was following the book perty close warm up the engines at or below 2000 rpms .then dont stay at any given speed for very long after a 1/2 hour i went up to 2800 and back down to 500 rpms then after the 1.5 hours i went to 3500 and back down to 500. then back up to 4000 after the 2 hours plus for about 1 min. I have 5 hours now and havent been past 5000 rpm. I think it is tim to try to reach 6000 and trim it up . If i dont get where i want to be on rpms and mph i will sell this prop. Thanks for your input

packer · 06-09-2009, 06:21 PM

One trick to use when learning to trim your boat is after each trim adjustment make a good solid turn , if the motor is trimed to high the prop will cavitate . After a few runs you will figure out where to set it for different loads and seas

cloudbusterb · 06-10-2009, 02:30 PM

does your kicker motor ride low in the water off the swim step on the north river or do i need to jack it up a big wave over the back will samp that engine

lurking_out_loud · 06-11-2009, 08:28 PM

On my 21 I used a 14.5x21 SWS prop and got great results. Depending on what prop you have, stainless, aluminum, SWS1, or SWSII your performance will really vary. I think being mounted on the first hole may have your motor too low and creating more drag than usual (my 225 was on the 2nd hole). Without trimming the engine up you are also pushing the bow down and killing speed as well. The total load in your scenario is also a bit high.

So, try it again with just a couple of people not the whole extened family. Play with the engine trim and see how it affects your RPMs, handling and the ride. If the boat surges up and down, you have gone too far up. If the boat feels like its pushing water its trimmed too low. What you will find is that the boat will have a sweet spot where it moves efficiently and easily. On my Seahawk, the RPM sweet spot was between 3600 and 4000rpm with the engine trimmed up a couple of led bars.

I'd go out again and just play around and get a feel for what engine trim and your trim tabs do for your ride. If you still can't get to the top RPM range you are looking for, then look at your engine mounting height and prop selection.

-lol

cloudbusterb · 06-15-2009, 09:24 PM

Quote:

Originally Posted by lurking_out_loud

On my 21 I used a 14.5x21 SWS prop and got great results. Depending on what prop you have, stainless, aluminum, SWS1, or SWSII your performance will really vary. I think being mounted on the first hole may have your motor too low and creating more drag than usual (my 225 was on the 2nd hole). Without trimming the engine up you are also pushing the bow down and killing speed as well. The total load in your scenario is also a bit high.

So, try it again with just a couple of people not the whole extened family. Play with the engine trim and see how it affects your RPMs, handling and the ride. If the boat surges up and down, you have gone too far up. If the boat feels like its pushing water its trimmed too low. What you will find is that the boat will have a sweet spot where it moves efficiently and easily. On my Seahawk, the RPM sweet spot was between 3600 and 4000rpm with the engine trimmed up a couple of led bars.

I'd go out again and just play around and get a feel for what engine trim and your trim tabs do for your ride. If you still can't get to the top RPM range you are looking for, then look at your engine mounting height and prop selection.

-lol

cloudbusterb · 06-15-2009, 09:25 PM

i will try it this week. Thanks for all your help