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Prop Selection

Printed From: The Fishing Website
Category: General Forums
Forum Name: The Boat Shed
Forum Description: Discuss all things boating.
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=1451
Printed Date: 25 May 2024 at 12:51am


Topic: Prop Selection
Posted By: obald
Subject: Prop Selection
Date Posted: 06 May 2003 at 10:25pm

This has arisen from a thread that I think started with pics of Lethal's boat. I'm sufficiently ignorant to want to have it dealt with as a thread in its own right.

If you decide you need a 'bigger' (or 'smaller') prop in any situation, how do you decide whether to increase (or decrease) the pitch or the diameter? And to further complicate things, what determines how many blades are best for your requirements and what blade shape is best? How do you factor propeller slip into all of this? Or is it best just to stick with the thing that was bolted onto the bottom of the leg when you bought it?

obald




Replies:
Posted By: Naki
Date Posted: 07 May 2003 at 7:48am

Hi.

In the latest Propeller Mag there is a test on various props. Not really sure what can be taken from this exercise tho. Every boat and every situtation are different. I surppose what you need to do is do some tests in flat water at different speeds recording revs, trim, fuel comsumption and then try different props and compare. Check your manual and find out what the max rev range is.

For all you Yammie owners out there try this site for performance figures.

http://www.yamaha-motor.com/products/otb/perfbull/performance_02.html">http://www.yamaha-motor.com/products/otb/perfbull/performance_02.html

 

Cheers.



-------------
President of the "Pontoon Owners Club".
I started off with nothing and now I still have most of it left!!!


Posted By: Martini Max
Date Posted: 07 May 2003 at 1:45pm

 Gidday,  I have tried 4 different props on my tub, as I was dissappointed with the reverse.  My Yam. Dealer and I spent an arvo out at Lake Karapiro testing them,and tho I don't have all the info (He may), what we found was that basically, the standard Yam prop is pretty darn good . Now, I don't remember the brands of other props, but one we tried, for example, was a little smaller. This got us up on the plane quicker, as it built revs quicker, and had more slip. (I have to be careful with the facts and my memory here, but I still hope it demonstrates the differences). In medium and high speed turns, it tended to cavitate or aerate much more, as it couldn't "grip" in the water as much. Would be ok for towing a skier if one was into that.    Next we tried a 4 blader. It looked  waaayy cool , but was expensive.  It was of comparitive size as the stock prop. Outa the hole it 'felt" good. Acceleration good, and stuck well in turns, ie good "grip".  In reverse was also good.  (the first, no real difference if not a little worse). We tried one other,with more pitch, nothing spectacular with it, it did the job. I don't think this one allowed us to pull max rpm. The 4 blader made the boat feel very "solid" in the water.Back to the standard one. This got us out of the hole well (comparatively), slipped a little in turns, (trimming motor down limited this) , and we could pull into the max. rev range. It reversed better than the others, excepting the  sexy polished stainless 4 blader, just had to give it a few more herbs and trim UP a little for best results. It also gave the best all round fuel figures, and speed/rpm  results.   I've talked to another bloke about poor reverse, he has installed motors on mussel barges in the past. With thru hub exhaust, the water was very aerated (For reverse), they put on larger props, drilled the prop to relieve the exhaust pressure out the back when in reverse,and found  that  that did the trick. No problems in forward.   As this sort of demonstrates, it can be a very complex subject, and in the end the stock prop makes the best all round deal. The best would've been the 4 blader, but at over  grand, didn't make a grands worth of difference. Sure looked good tho.  Sorry 'bout the long post if ya got this far. Cheers.

 

 



-------------

"I do nothing..I do it well.. I then move on to doing more of nothing"


Posted By: Lethal
Date Posted: 07 May 2003 at 2:46pm

Thats interesting stuff Martini Max.......

i know a guy down in Howick that fixes and rebuilds props i took my Yamie in to be repaired just a 90hp and he asked me at the time what rev's i was getting,  which was around 5.100 to 5.200  will get you a bit more he said, it should be just under 6000 when i got it back and tried it thats were it went to 5-800 to 5-900...... im sure there are other guys around that if you ask im sure they can fix these problems with your normal prop without going to the expence of a new one........ 

Cheers Lethal




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