40 HP Mercury Prop Damaged & Ventalating; low WOT

dwarner80

Recruit
Joined
Jul 29, 2012
Messages
4
I'm new to boat owning and purchased a 16.5' pontoon w/ a 40 HP Mercury which currently has a bent/cracked fin on the prop. I've noticed several things running this boat around on the first trip:
  1. it ventalates if it's not trimmed almost the whole way down
  2. WOT is ~4900 RPM; the engine's Max RPM is 5500
  3. the engine shudders at < ~1300 RPM (not convinced this is a prop issue, though)

Some other info from the sticky:
  • current prop is aluminum; I believe it's a 11 5/8" x 13p (the sticker on the engine says 13x26 which I can't believe; I think the max I could fit is a 12")
  • WOT was ~4900 at 15.9MPH on the GPS w/ light load (2 people)
  • 2003 40HP Mercury 2-cycle; 2.00 gear ratio
  • 16.5' Pontoon boat; ~1700lbs

Let me know what other info is needed; thanks!
 

dwarner80

Recruit
Joined
Jul 29, 2012
Messages
4
Re: 40 HP Mercury Prop Damaged & Ventalating; low WOT

Attached are some pics of the current prop.
2012-07-29 20.35.30.jpg
2012-07-29 20.26.39.jpg
2012-07-29 20.26.21.jpg
 

Expidia

Commander
Joined
Aug 26, 2006
Messages
2,328
Re: 40 HP Mercury Prop Damaged & Ventalating; low WOT

Google prop repair or check iboats they may have a link to a prop repair. I've sent mine out two different times. Cost about $28 plus $10 return shipping. Prop comes back looking like new. Takes a week or two.

This might be a good time to invest in a spare prop. This way you have a spare onboard if you hit something. Buy a $10 plastic prop wrench and an extra prop nut and the tab washer too. You need to put about 55 lbs of pressure when you tighten the prop nut. The tab washer has two tabs that you bend up along the flat side of the nut. It also sits on two nibs which precvents it from turning.

If you don't get around 55 lbs (you can buy a cheap torgue wrench at like Harbor Freight or order it online. I bought a cheap one at sears. Or you will be posting back in a thread "I put a new prop on and it spun off???"

This way if you have to send your prop out you have your spare for boating the next few weekends.

I'd by the OEM one by Mercury Quicksilver. If you buy another brand some make you also buy a hub for like another $30 that fits inside.
I got stuck with a Michigan Wheel one and it's a pain having to fit the hub together and keep track of the hub parts when I have the good OEM Merc one on. I didn't know any better or was trying to save like $20 bucks at the time. The Marina guy never told me the difference between a built in hub or the Michigan Wheel hub adapter for my 40 hp Merc. A prop repair shop can also sell you a spare if they have one in stock but summer I'm sure they are harder to get.. A new OEM one is like $124, just shop around a little. Beware of Marinas selling you a rebuilt prop as new since its hard to tell the difference. Make sure it comes with an undamaged matching box.

I think iboats also price matches. I know West does. That's the only way I'd ever buy from West as they are very high on everything other than their flyer specials.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: 40 HP Mercury Prop Damaged & Ventalating; low WOT

I think you need to go with a 4 blade 10" pitch Solas Amita prop.
You could get your prop repaired And do some test runs and get us the numbers.
I'm pretty sure you'll need that 10" 4 blade. You can then keep the 13 as a spare.
The 4 blade will resist venting,run smoother and respond better around the dock.
 

dwarner80

Recruit
Joined
Jul 29, 2012
Messages
4
Re: 40 HP Mercury Prop Damaged & Ventalating; low WOT

How can I tell what pitch I currently have for sure? To be honest, the only place I've seen "13" is on the sticker, and I believe that refers to the diameter (which it obviously can't). The stamp on the prop says "48-827312-10.5"; is the "10.5" the current pitch?
 

Georgesalmon

Lieutenant Commander
Joined
Apr 14, 2012
Messages
1,793
Re: 40 HP Mercury Prop Damaged & Ventalating; low WOT

yes 10.5 is current pitch.
 

dwarner80

Recruit
Joined
Jul 29, 2012
Messages
4
Re: 40 HP Mercury Prop Damaged & Ventalating; low WOT

Doing some research on this part number it's feeling more and more that the prop I have is a 11 5/8" x 10.5p. I read somewhere else that a damaged blade can definitely cause ventilation problems, but would I expect it to also drop my WOT RPMs? Should I just try getting a new QA2066X and have my old one replaced?
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: 40 HP Mercury Prop Damaged & Ventalating; low WOT

The best way to do this is to get the prop repaired if possible and cost effective and get new test data.
Yes a damaged prop can cause slip and ventilation also could create drag.So results from a damaged prop
isn't really predictable.
I still think a 4 blade will out perform a 3 blade all the way around.
The Soplas Amita have been predictable,good performers.
Assuming the old prop was right when installed I think a drop to a 10" would be in order for a 4 blade.
 

Mi duckdown

Commander
Joined
Apr 14, 2007
Messages
2,575
Re: 40 HP Mercury Prop Damaged & Ventalating; low WOT

Get the prop repaired and report back. If it shudders at any Speed You will have lowerend problems down the road.
 
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