prop stainless vs alloy

ian parkes · 30 July 2007, 22:01

A local chandler has a stainless prop , genuine suzuki to fit my engine at a very good price .
Am I likely to see any advantage with a stainless prop on a 70 hp engine , other than the fact thats its more robust .

bedajim · 30 July 2007, 22:03

Quote:

Originally Posted by ian parkes

other than the fact thats its more robust .

Does that work against the gearbox if you hit something

Downhilldai · 30 July 2007, 22:41

Quote:

Originally Posted by ian parkes

A local chandler has a stainless prop , genuine suzuki to fit my engine at a very good price .
Am I likely to see any advantage with a stainless prop on a 70 hp engine , other than the fact thats its more robust .

If I were you, I would only buy this prop if it is a fully verified 18" pitch

Mollers · 30 July 2007, 22:57

Quote:

Originally Posted by Downhilldai

If I were you, I would only buy this prop if it is a fully verified 18" pitch

......and then send it up to 'me Joolie' for some treatment.

Nos4r2 · 30 July 2007, 23:12

Have you ever dinged your ally prop? If you have I'd agree with Bedajim.A gearbox is a lot more money than a prop.

xtreme · 31 July 2007, 00:03

Hi guys,

I run a 11m rib with twin 250hp outboards in cardiff we take people out for fast rib rides.... On sunday i was on my way back to the marina and i struck an object floating just under the water i did not think it was that bad untill i lifted the boat out this morning and found that i had bent my stainless prop which in turn bent the prop shaft!!!!!!. Stainless props are not forgiving please stick with your ali prop it will save you a lot of money i am looking to get some made up for my boat ....

Ryan ...

codprawn · 31 July 2007, 00:07

Remember it may officially be summer but the rivers still look like they do in winter - they are carrying a LOT of tree trunks and logs out to sea. Just cos the sun has come out doesn't mean the logs have gone!!!

Shame about your engine. I also wonder about the so called advantages of stainless props - maybe it's because they are nice and shiny???

simmons0 · 31 July 2007, 00:21

But then if you'd of hit that submerged object with an Ali prop it might of damaged the propeller so much it wouldn't of got you home had you been a single engined boat.

codprawn · 31 July 2007, 00:34

Quote:

Originally Posted by simmons0

But then if you'd of hit that submerged object with an Ali prop it might of damaged the propeller so much it wouldn't of got you home had you been a single engined boat.

I think that would be pref to a bent shaft - OUCH!!!

simmons0 · 31 July 2007, 00:36

Depends where you are

xtreme · 31 July 2007, 00:39

u should have a spare set of props i carry 2 spare stainless props and pins + nuts if i only had 1 engine i would defo have a spare aux outboard 3-5hp

ian parkes · 31 July 2007, 00:45

Well its not much dearer than an ally prop , and 19" which is what I have now (good for cruising) thought maybe it was a good bet and if the performance was better with stainless , I dunno maybe cos its thinner or sharper etc , then could go somewhere towards my 18" pitch ideal.

I thought the rubber bushed hub was supposed to fail before the shaft or gearbag got damaged .

i guess the old shearpin had its advantages .

xtreme · 31 July 2007, 00:52

all i can say is if u want this prop get it but if you do hit anything it will hust (your pocket)

all the best guys if you want a ride on the boat if ur in cardiff pm me

ryan

xtreme · 31 July 2007, 00:53

that was ment to say hurt

Spike · 31 July 2007, 01:13

Hi Ian,
Just looking at your above post & you say your pushing a 19" alloy prop with a Suzi DF70 on a 4.7ish boat.....what are your rev's at WOT? Im running a 14" stainless with a Yam 60 on a 4.8 boat & not hitting top revs but i get v-good all round performance, i can only get to top rev's with an alloy 14" but that gives me poor 'out of the hole' performance but great top end, good if the sea is mirror flat but crap in a big sea. Just sounds to me like your well over proped on your boat currently......i could be wrong though but it would be interesting to know what revs your pulling WOT & your current top speed before you puchace the new prop.

bedajim · 31 July 2007, 07:18

Quote:

Originally Posted by ian parkes

i guess the old shearpin had its advantages .

Yep and there was normally a spare under the cowl

ian parkes · 31 July 2007, 10:49

Quote:

Originally Posted by Spike

Hi Ian,
Just looking at your above post & you say your pushing a 19" alloy prop with a Suzi DF70 on a 4.7ish boat.....what are your rev's at WOT? Im running a 14" stainless with a Yam 60 on a 4.8 boat & not hitting top revs but i get v-good all round performance, i can only get to top rev's with an alloy 14" but that gives me poor 'out of the hole' performance but great top end, good if the sea is mirror flat but crap in a big sea. Just sounds to me like your well over proped on your boat currently......i could be wrong though but it would be interesting to know what revs your pulling WOT & your current top speed before you puchace the new prop.

This prop science seems to vary a lot . My max recomended rpm is 5800
The boat came with a 17" pitch fitted . With that prop it would pull 5800 at 36mph loaded with 3 people full fuel etc but it was a bit lively with less load and tended to over rev a little .

I then fitted a 19" pitch which gave more relaxed cruise but would only pull 34 mph at about 5300 rpm same load .

From that I figured an 18" pitch would be ideal ,but an 18" isn't available . Iam now waiting to try the original 17" prop which I has been re pitched to 18

My thoughts with the stainless 19" that is on offer were that if stainless gave better performance it may just do the job allround and I would also have a spare prop or two. Its just expensive trial and error it seems .
Not sure what dia your prop is mine is 13 1/4 " maybe thats the difference .

ian parkes · 31 July 2007, 10:50

Quote:

Originally Posted by Spike

Hi Ian,
Just looking at your above post & you say your pushing a 19" alloy prop with a Suzi DF70 on a 4.7ish boat.....what are your rev's at WOT? Im running a 14" stainless with a Yam 60 on a 4.8 boat & not hitting top revs but i get v-good all round performance, i can only get to top rev's with an alloy 14" but that gives me poor 'out of the hole' performance but great top end, good if the sea is mirror flat but crap in a big sea. Just sounds to me like your well over proped on your boat currently......i could be wrong though but it would be interesting to know what revs your pulling WOT & your current top speed before you puchace the new prop.

This prop science seems to vary a lot . My max recomended rpm is 5800
The boat came with a 17" pitch fitted . With that prop it would pull 5800 at 36mph loaded with 3 people full fuel etc but it was a bit lively with less load and tended to over rev a little .

I then fitted a 19" pitch which gave more relaxed cruise but would only pull 34 mph at about 5300 rpm same load .

From that I figured an 18" pitch would be ideal ,but an 18" isn't available . Iam now waiting to try the original 17" prop which has been re pitched to 18

My thoughts with the stainless 19" that is on offer were that if stainless gave better performance it may just do the job allround and I would also have a spare prop or two. Its just expensive trial and error it seems .
Not sure what dia your prop is mine is 13 1/4 " maybe thats the difference .

ian parkes · 31 July 2007, 10:53

sorry posted twice don't know how that happened , had to re log twice ?

Spike · 31 July 2007, 11:52

Hi Ian,
Rule of thum is you go down one pitch to achive the same performance when going from alloy to stainless the difference is the stainless prop is probably cupped & definetly has thinner blades so will load up a lot better thus giving a lot better performance with no slip (you could also try lifting your engine one bolt hole to gain better top end), If you go for a four blade then it will also give you better 'bow lift' & hold you on the plane at slower speeds. Also forget the max RPM what you need to know is at what rev's you get max BHP this will lower than your max rev's & this is where you want to be when you have a loaded boat. Personally if i where you i would go for a 17" four blade prop from Steel Developments they will alter the pitch up or down for you that way you should gain back some of your top end but still gain benifits lower down the rev range as well, should be better on fuel than 19" too as IMHO the engine will labour to much trying to turn a 19" prop in any sea state other than mirror flat.