props

[yam90]

could someone please explain the benefits of a stainless steel prop with four blades as opposed to an aluminium prop with three. apart from the obvious strength factor?.
cheers

[Wahoo]

could someone please explain the benefits of a stainless steel prop with four blades as opposed to an aluminium prop with three. apart from the obvious strength factor?.
cheers


yam 90, shoot Scott (FNQ Cairns) a pm, he knows his stuff when it comes to props;)

Daz

[FNQCairns]

The most efficient prop is one that would have 1 blade, 2 is more efficient than 3, 3 than 4, 4 than 5.

The extra blade allows for a very nicely balanced propeller in comparison to 3 blades.

Bottom line is many 4 blade props can be emulated in their behaviour by a low performance (high surface area to diameter) 3 blade.

A well chosen 3 blade will give the same low speed holding power and better top speed than a 4 blades will.

cheers fnq

[FNQCairns]

yam 90, shoot Scott (FNQ Cairns) a pm, he knows his stuff when it comes to props;)

Daz

Thanks Daz very kind but probably not true,

cheers fnq

PS about polishing that black donk of yours again, what time will you be home tommorrow;D

[Wahoo]

PS about polishing that black donk of yours again, what time will you be home tommorrow;D

LOL Scott, if you were out with us yesterday, you would of used sandpaper to wipe the motor down, not a good day

Daz

[FNQCairns]

Daz, that's a shame, on the bright side the odds are now better for a trouble free next trip:)

cheers fnq

[disorderly]

not a good day

Daz

Uh Oh, dare I ask?

[Wahoo]

Uh Oh, dare I ask?

Well Scott

started off with seebreez 5-10::), so i changed props 17p to 19p to get some figures before i take it in to reshape the 19, did'nt have a chance in hell to use WOT >:( swell was big and blowing 15+ knts used 140lts fuel covering 190Ks with that damn prop>:(, lost a shit load of gear dew to quite a few rather largeish sharks, and not a great deal of fish and thats 10hrs on the water, lines were getting tangled left right an center, just one of them days if you know what i mean Scott


Daz


Yam90, sorry about the highjack mate

[FNQCairns]

Uh Oh, dare I ask?

Phew! glad you did, I was too scared to ask, visions of supercharger pieces flying through the air filled my imagination:).

Sounds to me like a fairly typical fnqcairns offshore trip, minus almost sinking without the bungs, argument with the deckie because of the work involved in pulling up float pulled anchors and fuel load miscalculations of coarse:)

cheers fnq

[Dan5]

I can vouch for FNQ's fuel calculation's LOL.

[disorderly]

I can vouch for FNQ's fuel calculation's LOL.

Scott ,the secret to fuel miscalculation is never admit it to your deckie unless you ACTUALLY run out of fuel.If you arrive back at the dock with 0.5 of a litre of fuel left, than that it is a perfectly planned triphttp://www.ausfish.com.au/vforum/../yabbfiles/Templates/Forum/default/wink.gifhttp://www.ausfish.com.au/vforum/../yabbfiles/Templates/Forum/default/grin.gif.
Dan, it sounds like you and FNQ had a really well planned triphttp://www.ausfish.com.au/vforum/../yabbfiles/Templates/Forum/default/grin.gif.

Scott

[Dan5]

Well if returning with 0.5 ltrs is "perfectly planned" then thats what it was "perfect".Naa we had enough just not as much as we would have liked to go abit further,all was good FNQ just chewed his finger nail's to the first knuckle that's all!Dan..............

[disorderly]

Well Scott

started off with seebreez 5-10::), so i changed props 17p to 19p to get some figures before i take it in to reshape the 19, did'nt have a chance in hell to use WOT >:( swell was big and blowing 15+ knts used 140lts fuel covering 190Ks with that damn prop>:(, lost a shit load of gear dew to quite a few rather largeish sharks, and not a great deal of fish and thats 10hrs on the water, lines were getting tangled left right an center, just one of them days if you know what i mean Scott


Daz


Yam90, sorry about the highjack mate

Daz,sounds like you had an absolute dog of a day!!
I only fish 2 persons in my boat!!I only have a runabout and seriously hate tangles and fighting over who grabs the rod with the spanish mackeral on the floater. http://www.ausfish.com.au/vforum/../yabbfiles/Templates/Forum/default/rolleyes.gif

Scott

[FNQCairns]

I can vouch for FNQ's fuel calculation's LOL.

That bloody Navman fuel computer told me I was using 4L hour at WOT and 2L at cruise.....that's my excuse...how embarrassment:-[.

[Dan5]

4ltrs per hr? when did you get a 250 e-testicle!

[trueblue]

could someone please explain the benefits of a stainless steel prop with four blades as opposed to an aluminium prop with three. apart from the obvious strength factor?.
cheers

Strength really isn't an issue, and if you have a stainless prop and hit a rock you stand real chance of wrecking the gearbox shaft because the prop will just bend a bit and put most of the force into the shaft before the bush spins out. With an alloy prop, the blades will just break off. So for a tinny in creeks etc around rocks and logs etc I would only use an alloy prop.

An alloy prop is also more than strong enough to do its job, will just wear out a bit quicker, but it is a lot of miles in clean water to wear one out.

Stainless props are a touch thinner than the alloy ones which slightly increases their efficiency, but very marginal.

4 and 4+ blade props have good points and bad points. Bad point is that they tend to slip a lot in reverse so you have to really get to know your boat and its new limitations in reverse when you fit a 4 blader.

A good point about a 4 blader is that it can give some extra 'lift' at the stern of a boat that won't be happening with a 3 blader. Don't know why - but have extensively tested lots of props on my boat (at least 7 prop and or cupping options) and the 4 blader lifts my boat up about 3/4" on the plane compared to the 3 blade.

4 bladers are very good in surging seas. They get much more bite on the water and therefore you can often set the throttle much better and just ride the boat in surging seas instead of constantly being on and off the throttle. (Although there are now some wide blade 3 blade props that do much the same).

4 Blade props can cost you fuel efficiency if not absolutely perfectly tuned to the size, weight and power of your boat. As lots of prop makers jump up in pitch by 2" at a time, it can often be hard to get exactly the right pitch (Like for my boat - I really needed a 16" pitch but 15 and 17 were the only options so I have a modified and cupped 15" pitch that gives approximately 16" of pitch but costs me a little top end speed with the bonus of better anti cavitational properties).

Its actually a fairly complicated science as I found out when playing with props, and the differences are not always immediately obvious till you have run the prop on several long trips and felt the boats performance in various seas and measured its economy.

Biggest differences in props that are worth chasing in my opinion are handling in rough weather. I thought I had a winner with one prop that I tested that had good fuel economy but the draw back was that it was a pig in big waves and constantly broke loose.

You really need to test in flat seas, moderate chop and rough seas (into and following) to really know if a prop selection is right for your boat.

cheers

Mick