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Old 28 November 2004, 17:23   #1
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repacement prop required help

i want to change my prop to a stainless steel type to cut cavatation in tight
turns down when the prop loses grip

ive been told a alloy prop will not grip as well as ss type and are much better
in the water all round

my engine is a 50hp 2003 mercury elpto which as a unknown prop fitted

down the side is the numbers 4873136a40 13p i think hard to read to much paint

it will rev at 5900 wot which is a bit high so could be dropped a bit
i don,t need to go any faster or carry more weight the boat is fine apart from the turns

so what ss prop do i go for how much are they were do i find the best deal

all i know is i think its a 13

any help or contacts

i am all so off to see mickey mouse in the states in jan so is it worth getting
a mercury prop out there ive seen then at about $100 on the net would any one know the part numbers of replacement ss mercury props

thanks dan
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Old 28 November 2004, 17:27   #2
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Dan

Give Steel developments a ring, the owner is a very helpful bloke with a wealth of knowledge. Number is on here somewhere, as well as a link to his website.

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Old 28 November 2004, 17:32   #3
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i am going to send my old one back to them for a refurb after a fit my new one are there new ss props as good as the mercury ones ?
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Old 28 November 2004, 17:38   #4
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Don't turn Dan.problem solved.
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Old 28 November 2004, 17:43   #5
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Sorry Dan, on a serious note I recieved an E-Mail from boats and outboards last week,some guy who breaks outboards is selling of a load of stock, I have deleted the E-Mail but will look at site for you.There you go mate found it, good luck.


Bill Higham Marine
The Chapel, City Road, Worsley, Manchester
M28 1BD
Tel: 0161 790 7678
Web: http://www.billhigham.co.uk
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Old 28 November 2004, 18:34   #6
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Dan,

You’re suffering from ventilation in the turns not cavitation. As you go round the corner the prop moves closer to the surface and air then gets sucked into the prop resulting in a loss of grip.

A stainless prop won't solve your problem, although it may recover a fair bit quicker. I suspect you’re not trimming the engine in far enough during the turn. However if you still experience ventilation when the engines fully trimmed in then you might want to try lowering the engine on the transom.

Don't let me put you of a SS prop though. They do perform much better generally; however I wouldn't expect it to solve your problem. As Nasher says give Steel developments a ring. http://www.steeldevelopments.co.uk

From that serial number I would guess its a 13" pitch
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Old 28 November 2004, 18:57   #7
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I'd be blowed if I can tell the difference between my 17" SS and 17" Alloy prop. They are both Michigan wheel props the SS one being the raptor and the Alloy being a "Match" direct replacment one. Engine revs slightly higher with the Alloy but top end speed and handling are identical!
I guess on a sub 100hp Rib it dosn't make that much differance really, or if it did would it be worth the extra money for the gain in performance?

Not in my case anyway! I was told by my service centre that if you had an underwater collision with a SS prop, it'll be a new gearbox but much less likley with a Alloy prop. Reason enough to stick to Alloy props.

Andy
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Old 29 November 2004, 05:04   #8
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Hi Daniel and Dan,

Daniel,

I have had a much better experience when I went from an aluminium prop to a Stainless one on my 5.4m Searider with a 90hp. Was suffering from ventilation/cavitation/loss of grip in turns and at high speed when trimmed right out.

Changed from a 19" aluminium standard prop to a 20" SS Laser II. The difference was incredible. Could turn much tighter, could trim the engine up as much as I wanted without losing grip.
The point is that the Laser II is a high rake propeller with a large amount of cupping on the trailing edges of the blades and is designed to run in aerated water near the surface. I feel that this is why it works well, not necessarily because it is SS.

My Scorpion has a 19" SS Mercury Vengence prop at the moment. This seems to ventilate / cavitate a fair bit under certain circumstances. Over the next season I shall be looking to try some alternative props - probably 19" and 21" Laser IIs to see if there is any improvement.

There were other issues with my aluminium prop. There were numerous fractures in the blades that may have been allowing flexing and had I changed to a new aluminium prop this may also have restored the performance to what it was when I bought the boat.

So, Dan, is your current aluminium propeller in good condition? If not, then it might be worth getting it overhauled by someone such as Steel Developments. In any case this can't do any harm.
If you want to bring your revs down a bit then you need to increase the pitch. By how much, however, is where the guesswork starts. Many will quote rules of thumb of about 1" reducing rpm by a few hundred and if going from aluminium to stainless to add an inch on top of that.
In my experience in going from a 19" aluminium to a 20" stainless made no difference in the maximum rpm.
So maybe try a 15" stainless prop with lots of cupping.
Or a selection of secondhand aluminium ones from Bill Higham might work?

Finally, a shiny stainless prop looks fantastic and we must not forget that one of the reasons for having a boat is in the pride of ownership.
Never underestimate the importance of bling!

If you can get a cheap Mercury ss prop when you go to the States then why not? There is some information on Mercury props on the mercurymarine.com website.

Regards
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Old 29 November 2004, 06:54   #9
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Quote:
Originally Posted by Searider

Finally, a shiny stainless prop looks fantastic and we must not forget that one of the reasons for having a boat is in the pride of ownership.
Never underestimate the importance of bling!

If you can get a cheap Mercury ss prop when you go to the States then why not? There is some information on Mercury props on the mercurymarine.com website.

Regards

If this is the case then why not just spray your ally prop silver best of both worlds then, the "bling look" (if thats important to you) and a prop that wont wreck your gear box when you hit the bottom
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Old 29 November 2004, 07:01   #10
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Quote:
Originally Posted by DJL
Dan,

You’re suffering from ventilation in the turns not cavitation. As you go round the corner the prop moves closer to the surface and air then gets sucked into the prop resulting in a loss of grip.

A stainless prop won't solve your problem, although it may recover a fair bit quicker. I suspect you’re not trimming the engine in far enough during the turn. However if you still experience ventilation when the engines fully trimmed in then you might want to try lowering the engine on the transom.

Don't let me put you of a SS prop though. They do perform much better generally; however I wouldn't expect it to solve your problem. As Nasher says give Steel developments a ring. http://www.steeldevelopments.co.uk

From that serial number I would guess its a 13" pitch

i looked at were the engine was mounted and set up. the engine can not be lowered at all as its sitting on the transom and i checked the mercury install guide and it meets that and i don,t want to cut the transom down so a stainless steel seems to be the way to go for improving the turns

thanks dan
my alloy prop may be damaged but not that i could see it look in good nick
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