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  170 Montauk 90 HP - What aluminum prop?

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Author Topic:   170 Montauk 90 HP - What aluminum prop?
bben posted 08-29-2012 09:52 PM ET (US)   Profile for bben  
Hi all, I was wondering what aluminum prop recommendations you have for my 2008 90HP 170 Montauk? I run it in the Keys with a lot of shallow water. I want to maintain as much of the same charateristics as the stainless prop as possble. Thanks.
L H G posted 08-29-2012 10:46 PM ET (US)     Profile for L H G    
For aluminum, I would try the brand new Mercury Spitfire 4-bladed prop in 19" pitch. See here:

http://www.mercurymarine.com/propellers/aluminum/spitfire/

This guy has very good shipped pricing, including hub kit($149):

[url]jacosmarine.com{/url]

Or you could use the BlackMax 21" 3 blade aluminum. They are remarkably good performers. If you don't need a hub kit, this guy has the best pricing shipped:(the Quicksilver version is the same as the Mercury version) ($103)

http://www.dansdiscountprops.com/BuyNow/Quicksilver.cfm#QuicksilverA

Jefecinco posted 08-30-2012 09:52 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Bben,

I suggest you buy at least two aulminum propellers. Using an aluminum propeller in the shallow water of the Keys will almost certainly result in having one or more of them in the shop for a good bit of time. It would be prudent for you to carry a spare propeller aboard when using aluminum in shallow water.

A stainless steel propeller may cost more but will provide much better value over time.

Butch

bben posted 08-31-2012 01:51 PM ET (US)     Profile for bben    
thank you both
swist posted 08-31-2012 05:07 PM ET (US)     Profile for swist  Send Email to swist     
I tried to do some math on this years ago for the same reason (is it more cost-effective to run an aluminum prop in areas where the prop is more likely to hit something) and found it was pretty complicated. It involved the repair costs of aluminum vs stainless, the types of dmanage that could be repaired vs replaced on the two types of metals (not the same), the decision on whether to have a second aluminum prop available, the types of object strike that would in fact cause no damage to stainless vs aluminum, and the performance differences between the two, possibly also affecting fuel cost.

I gave up and stayed with an aluminum plus backup on my earlier boat. Now I have a stainless with no backup in the same waters, and I still don't know the answer to the question.

bben posted 08-31-2012 07:46 PM ET (US)     Profile for bben    
It is a tough one. I have hit hard bottom with my stainless and bent the prop shaft, not too bad of a fix. Then, I went with an aluminum one and broke that one on less hard of a surface. It is a toss up. I don't like to be limited by the tides and shallows of the lower Keys so I am thinking to stay with the aluminum and carry the stainless as my back-up. I ran the aluminum one for a good 100 hrs before breaking one of the blades and that was my mistake. Thanks again.
swist posted 09-01-2012 09:13 AM ET (US)     Profile for swist  Send Email to swist     
I've had (1) hard strikes on the SS prop which caused no damage, and (2) at least one similar incident where there was no prop damage, but a slightly bent prop shaft). If the prop shaft is bent, slightly or non-slightly makes little difference, it's expensive). You can't always rely on that rubber grommet to slip enough and quickly enough to prevent shock from being transmitted to the lower unit.

So in the first case the SS prop saved the day. In the second case, it would have been much cheaper to repair an AL prop and have the shaft etc intact.

Keeping your speed down in shallow water obviously helps, but in the above two cases, it was deep water with timbers or logs floating just beneath the surface.

And as a final conundrum, my observation is that a planing hull can push a lot of objects out of the way, whereas at displacement speed you might run over them. But I'm not sure this translates into going faster when there's debris present.

Tom W Clark posted 09-05-2012 10:01 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The tired old argument that an aluminum propeller offers some protection to your drive train is a myth.

The ONLY thing an aluminum propeller does for you is save a little money up front but it will actually cost you more in the long run because they are so easy to damage you end up repairing or replacing them often, never mind the fuel economy and performance you give up when using an aluminum prop.

While it is perfectly true that propeller shafts can get bent if you have a hard grounding, the damage will occur with an aluminum prop just as easily as with a stainless steel prop.

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