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Old 11 May 2009, 21:16   #1
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Multiple props?

I acquired a demo 150 Yammie 4-stroke last fall, which came with a 13 3/4 x 19 prop. I wasn't sure what my old engine used but I noticed that the engine was a little sluggish out of the hole but very fast. I chalked this up to difference between the 4 stroke and my previous 2 stroke.

This weekend, just for fun, I tossed on my old prop... a 13 3/4 x 17. Immediately, I could feel a huge difference on "take off", but the boat was significantly slower... (New prop: 52 mph @ 5000 rpm, old one: 44 mph @ 5500+ ) This was slower than my old two stroke (also a 150) and I felt as though I was at risk of over-reving the engine.

I recall the installer saying that he had mounted the new engine "one hole higher" as it was rubbing a bit on the steering gear.

After this little experiment, I concluded that for day-to-day use (generally shorter trips with a load of dive gear) the 17 pitch might be best, but if I was heading out on a longer cruise where speed and fuel consumption might be more important, I would toss the 19 on.

So a couple of questions: Is this a reasonable approach? Or would I be better to get an 18 and split the difference? Should I consider dropping the engine a hole and see what happens?

I keep the boat on a trailer, so it's about a 3 minute job to change props...

Your thoughts would be appreciated!
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Old 12 May 2009, 02:25   #2
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Quote:
Originally Posted by Stoo View Post
I keep the boat on a trailer, so it's about a 3 minute job to change props.
I'd just change the props if you know what sort of use your doing.
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Old 12 May 2009, 09:07   #3
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Try a 4 blade. That will drop the revs slightly for the same size.
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Old 12 May 2009, 11:52   #4
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WOT RPM for a late model F150 is listed as 5000-6000 rpm. As you probably know, you ideally want to be able to hit the upper range of that.

I think the F150 has the same size gearcase as the F115, so you'll be limited to a 14" diameter max (as I recall; actually a bit less to avoid interference with the cav plate and zinc, so the 13.75 diameter is about max.)

Sounds like, despite the performance, the 19 is a little heavy, as you're barely reaching the max rpm range. Throw some more weight in the boat, and you'll be lugging it.

The 17 is closer, but it sounds like you need to look for different blade shapes that will bring back at least some of the performance loss between the 17 and 19.

The other option is to see if you can gain some revs with the 19 by dropping diameter a bit. Maybe a 13.00 or 13.25 x 19?


jky

p.s. Man, I wish someone would start throwing motors in my direction...
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Old 12 May 2009, 12:17   #5
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Hi guys
when I bought my boat from a skier it had a 'high five' on it was great out the whole but was hopeless at the top end where I wanted it for cruising. I changed back to the standard Mariner 3 blade 19 pitch and I now have the performace I want at the top and it gets me out the whole quick enogh to ski when we want.
Hope this helps.

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Old 12 May 2009, 12:40   #6
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Quote:
Originally Posted by Stoo View Post
I acquired a demo 150 Yammie 4-stroke last fall, which came with a 13 3/4 x 19 prop. I wasn't sure what my old engine used but I noticed that the engine was a little sluggish out of the hole but very fast. I chalked this up to difference between the 4 stroke and my previous 2 stroke.

This weekend, just for fun, I tossed on my old prop... a 13 3/4 x 17. Immediately, I could feel a huge difference on "take off", but the boat was significantly slower... (New prop: 52 mph @ 5000 rpm, old one: 44 mph @ 5500+ ) This was slower than my old two stroke (also a 150) and I felt as though I was at risk of over-reving the engine.

I recall the installer saying that he had mounted the new engine "one hole higher" as it was rubbing a bit on the steering gear.

After this little experiment, I concluded that for day-to-day use (generally shorter trips with a load of dive gear) the 17 pitch might be best, but if I was heading out on a longer cruise where speed and fuel consumption might be more important, I would toss the 19 on.

So a couple of questions: Is this a reasonable approach? Or would I be better to get an 18 and split the difference? Should I consider dropping the engine a hole and see what happens?

I keep the boat on a trailer, so it's about a 3 minute job to change props...

Your thoughts would be appreciated!
Stoo,
We did that for years,one prop to get to the place you wanted to ski,then the other to pull the chubsters out the water. Worked well for us.
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Old 12 May 2009, 15:03   #7
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Quote:
Originally Posted by IBWET View Post
...the chubsters out the water.
Funny that... my, main Buddy might be described as such as well. Hauling his butt back in over the toobs is becoming a bit of a chore. I've been considering installing a rubber grab handle like you would see on an inflatable onto the rear end of his drysuit so I have something to grab onto. I have also proposed using a gaff, but he is protesting about that...

Jambo, I see your engine and boat are about the size of mine and as I have thought about this, the 19 might be the better bet. I am assuming that fuel consumption is proportional to rpm more than speed, but as the price of fuel starts inching up again, that might be the deciding factor... Make do with the sluggish starts in order to save the fuel and to get where I'm going.

Honestly, this is the first time I've fiddled with props and I am surprised at the difference between the two...
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