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  Selected the wrong prop?

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Author Topic:   Selected the wrong prop?
billyc posted 06-29-2004 12:26 AM ET (US)   Profile for billyc   Send Email to billyc  
I recently purchased a SS prop and have found after two test runs at varying conditions that the motor exceeds max RPM at WOT.

Yes, I did read the reference section on props and many of the past forum discussions before I purchased this beauty. I realize that this is a worn topic, but I would like some advice from the experts who hang out at this site.

Here are a few details. The boat is a 2000 sport 13 with a 25 hp four stroke. It came with 13" pitch Al prop which I used for about 2 years. Mercury states that the full throttle RPM range for this motor is 5500-6000, and one should select a prop that operates in the upper half of this range. Under my typical load, the max RPM with the Al prop averaged 5400 with 24 MPH top speed.

I use the boat for fishing and usually launch close to where I plan to fish. Top speed is not that important, but I would like the boat to plane quickly and operate on plane in the 15-20 MPH range.

This spring I decided it was finally time to play with the prop selection. As an experiment, I purchased a composite prop with a 11" pitch. It worked great. Max RPM at 5800 and quick to plane. Max speed was about 22 MPH. I used it until it got chewed up on its first encounter with an oyster reef. At that point I decided to take the plunge and go SS.

I special ordered the SS prop from the Mercury dealer. I selected one with an 11" pitch based on previous experience. (Yes, I read the advice to go up 2" in pitch when going to SS, but figured that was based on much larger engines.) With this prop, the max RPM will stay a little over 6,000 with the engine trimmed all the way down. It will drift up to 6100-6200 RPM when trimmed up a little. I can comfortably cruise in the 5000-5500 range. The RPM alarm has not gone off, but I have not kept it above 6000 very long.

I figure my options are

a) Keep the prop... just don't operate at WOT.
b) Try to talk the dealer into exchanging it for a higher pitch prop (12" or 13"?) (They probably won't go for this since it was special order)
c) Keep the 11" pitch as a trailer hitch ornament and purchase a higher pitch prop the next time I have an extra $350.

Sorry about the length, but it was good therapy. If you are still reading this, what would you do?

Billy

Clark Roberts posted 06-29-2004 07:15 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Billy, what is top speed with the new SS prop? You say 6200rpm max with engine trimmed out but you don't say how much weight you'r carrying. If lightly loaded and only you in boat then I think you have the right prop. To be able to exceed max rpm a little when lightly loaded will mean that when you put more passengers and gear (and very hot weather) you will still be able to turn acceptable rpm. Overall performance and economy should, in my opinion, be better with the 11" SS prop. happy Whalin'... Clark... Spruce Creek Navy
If you go to a higher pitch prop you will need to go up only one inch (to a 12") since one inch of pitch will net approx 200rpm either up or down and in your case would dial it in at almost 6000 on the nose. Hey, your tach may be off by 200 rpm...
davej14 posted 06-29-2004 09:30 AM ET (US)     Profile for davej14  Send Email to davej14     
This is something I also have interest in because I just purchased an SS prop, waiting for delivery. Could someone with experience in repitching or adding cupping to an SS prop comment on the results as an alternative to just repurchasing another prop?

Also, if you decide to repurchase, check ebay because if you are patient you may save significantly. This is also an option to sell the prop you have, but you will take a significant hit.

billyc posted 06-29-2004 09:44 AM ET (US)     Profile for billyc  Send Email to billyc     
Thanks for your input. I tested with a normal load: two people, small ice chest, trolling motor and extra battery. I rarely go out with more than two in the boat (but have had five!).

If topping out at 6200 is no big deal, then I will keep the prop.

Bigshot posted 06-29-2004 09:50 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
They should & will exchange the prop for you...you might have to pay shipping. If they do not, never use them again because they charged you list price nd made at least $100 on your prop. If they chose not to exchange, have it double cupped by a prop shop. Real cheap and will add 1" of pitch and drop you a couple hundred rpms.
15ftlover posted 07-01-2004 11:22 AM ET (US)     Profile for 15ftlover  Send Email to 15ftlover     
I'm with Bigshot, you can get your prop cupped if the dealer doesn't offer a marginal restocking fee to swap out your SS prop. If not then get a reputable prop shop to recup and you may get RPM's down 200 or so.
Hen
Lopaka posted 07-01-2004 02:54 PM ET (US)     Profile for Lopaka  Send Email to Lopaka     
Heres a follow on question....whats wrong with keeping the current prop as is considering he did not test at maximum load. As he said he tested at normal load of 2 pax, extra batt and troll motor etc...but sometimes carries more? Is it ok to have the 6200 capability but just throttle back unless carrying a max load? Does running at 6200 actually hurt annything?
billyc posted 07-01-2004 03:59 PM ET (US)     Profile for billyc  Send Email to billyc     
Thanks, I appreciate the advice.
Mumbo Jumbo posted 07-01-2004 05:06 PM ET (US)     Profile for Mumbo Jumbo  Send Email to Mumbo Jumbo     
I have a 13' Whaler with a Yamaha four stroke 25. With one person and a full load of 12 gallons of gas, gear, pushpole, and two 25 qt. Igloos with ice I get a top speed of 27.5 mph with a PowerTech three blade stainless prop. Cruise is about 21mph. It is all I want for the 13 and the low end performance helps when two or three people are on board. The specs on the prop I use are:
PowerTech Marine
Model # YM30SRA3R11s-2
Stainless 3 blade, 10” dia, x 11” pitch with cup

http://www.ptprop.com/catalog/product_info.php?cPath=114_191_192&products_id=1265

Since you already have a 11" stainless prop which appears to be matched to your 13, you probably should keep it. You will lose low end performance if you re-pitch.

billyc posted 07-02-2004 12:22 AM ET (US)     Profile for billyc  Send Email to billyc     
Thanks. I decided to keep the prop and go fishing.

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