I currently have a 13.75 inch X 15 pitch aluminum prop on my 70 hp Evinrude. The prop was really beat to death by it's previous owner, and it is needing replaced. I use this boat for diving and skiing mostly, it runs about 30 knots at present, and yanks me up out of the water quickly. I was looking to go stainless, but they all seem to have a much higher pitch, like 19 or more. What could I expect from say 13.25 X 21? I would guess it would lug my motor down, and be very poor on pulling a skier up.
Rule of thumb with an I/O (so I've been told) ... if you use say a 21 aluminum, then use a 19 steel. In other words, decrease the pitch when switching to steel.
"gudmundur" <hexter@blazenet.net> wrote in message news:114mhnih09km73e@corp.supernews.com...> I currently have a 13.75 inch X 15 pitch aluminum prop on my 70 hp> Evinrude. The prop was really beat to death by it's previous owner, and> it is needing replaced. I use this boat for diving and skiing mostly, it> runs about 30 knots at present, and yanks me up out of the water quickly.> I was looking to go stainless, but they all seem to have a much higher> pitch, like 19 or more. What could I expect from say 13.25 X 21? I would> guess it would lug my motor down, and be very poor on pulling a skier up.>
It can't be that bad if you are still using it (although you probably shouldn't). You can get it repaired for a spare, or repaired and re-pitched for everyday use. Find a good prop shop and talk to them. There are a variety of factors that affect the performance of a prop. You can also have them add a "cup" or vent it, for example. Whatever you do you don't want to exceed your maximum RPMs at WOT and get a new - or repaired- prop on there right away!
If you are happy with the hole shot for skiing, you might be able to gain more top end with the right tuning with the prop you have. From your post it seems that you are unhappy with the top end speed but boat propellors rarely give you the best of both worlds.
Talk to the experts. It's well worth it.
Dan
gudmundur wrote:> I currently have a 13.75 inch X 15 pitch aluminum prop on my 70 hp> Evinrude. The prop was really beat to death by it's previous owner, and> it is needing replaced. I use this boat for diving and skiing mostly, it> runs about 30 knots at present, and yanks me up out of the water quickly.> I was looking to go stainless, but they all seem to have a much higher> pitch, like 19 or more. What could I expect from say 13.25 X 21? I would> guess it would lug my motor down, and be very poor on pulling a skier up.>
Rule of thumb with an I/O (so I've been told) ... if you use say a 21
aluminum, then use a 19 steel. In other words, decrease the pitch when switching to steel.<<
I'm not sure that's entirely accurate from my own experience. I had a aluminum 19 on my 190hp Merc and it ran WOT at about 5400RPM (when I bought the boat). The manual states 4400-4800rpm for WOT.
I read and heard that the adjustment was (rule of thumb) 1" pitch/200 rpms. So I increased the pitch to 23 with a SS prop, and I'll be damned if WOT is at about 4600rpm now...perfect. Maybe it would have been different if I stayed with aluminum, I don't know. YMMV
--Mike
"bowgus" <bowgus@rogers.com> wrote in message news:8NWdnf3wsc_M1tbfRVn-hQ@rogers.com...> Rule of thumb with an I/O (so I've been told) ... if you use say a 21> aluminum, then use a 19 steel. In other words, decrease the pitch when> switching to steel.>
"gudmundur" <hexter@blazenet.net> wrote in message> news:114mhnih09km73e@corp.supernews.com...>> I currently have a 13.75 inch X 15 pitch aluminum prop on my 70 hp>> Evinrude. The prop was really beat to death by it's previous owner, and>> it is needing replaced. I use this boat for diving and skiing mostly, it>> runs about 30 knots at present, and yanks me up out of the water quickly.>> I was looking to go stainless, but they all seem to have a much higher>> pitch, like 19 or more. What could I expect from say 13.25 X 21? I would>> guess it would lug my motor down, and be very poor on pulling a skier up.>>
I'm not sure that's entirely accurate from my own experience. I had a > aluminum 19 on my 190hp Merc and it ran WOT at about 5400RPM (when I bought > the boat). The manual states 4400-4800rpm for WOT.>
I read and heard that the adjustment was (rule of thumb) 1" pitch/200 rpms. > So I increased the pitch to 23 with a SS prop, and I'll be damned if WOT is > at about 4600rpm now...perfect. Maybe it would have been different if I > stayed with aluminum, I don't know. YMMV>
It's a 1995 Reinell 184 BRXL. Let me qualify that MPH statement. The stock speedo has seen 55 in smooth water and no wind. However, we know how accurate those things are. I'm going to use a GPS next time out and see what I really get. Prolly closer to 50. Bottom line really is that WOT is now within specs with the new prop, and she goes "pretty fast." <g>
--Mike
"trainfan1" <lmsearing@usdatanet.net> wrote in message news:CYSdnXAu48eUY9bfRVn-oA@usadatanet.net...> mgg wrote:>
I'm not sure that's entirely accurate from my own experience. I had a >> aluminum 19 on my 190hp Merc and it ran WOT at about 5400RPM (when I >> bought the boat). The manual states 4400-4800rpm for WOT.>>
I read and heard that the adjustment was (rule of thumb) 1" pitch/200 >> rpms. So I increased the pitch to 23 with a SS prop, and I'll be damned >> if WOT is at about 4600rpm now...perfect. Maybe it would have been >> different if I stayed with aluminum, I don't know. YMMV>>
It's a 1995 Reinell 184 BRXL. Let me qualify that MPH statement. The stock > speedo has seen 55 in smooth water and no wind. However, we know how > accurate those things are. I'm going to use a GPS next time out and see what > I really get. Prolly closer to 50. Bottom line really is that WOT is now > within specs with the new prop, and she goes "pretty fast." <g>>
--Mike
If you are running the 1.65:1 gearset, I think you'll find you're pushing 54-55 if your tach is right.
Assuming 10% prop slip, that's what I calculate also.
51 mph at 15 % , and 48 mph at 20%.<<
Would a SS prop reduce slip?
--Mike
"Wayne.B" <waynebatrecdotboats@hotmail.com> wrote in message news:2pgp41dm6pj0j27vjkee3sbmt2j9loisj7@4ax.com...> On Thu, 31 Mar 2005 21:23:59 -0500, trainfan1> <lmsearing@usdatanet.net> wrote:>
If you are running the 1.65:1 gearset, I think you'll find you're>>pushing 54-55 if your tach is right.>
================================>
Assuming 10% prop slip, that's what I calculate also.>
On Fri, 01 Apr 2005 06:12:07 GMT, "mgg" <mike@pacbell.net> wrote:
Assuming 10% prop slip, that's what I calculate also.>
51 mph at 15 % , and 48 mph at 20%.<<>
Would a SS prop reduce slip?
=================================
It's hard to say, but it might. The advantages of stainless over aluminum are structural rigidity (less flex) and surface smoothness (less friction). Improving either quality could decrease slip which would have the effect of increasing speed at comparable RPMs.
Short Wave Sportfishing 1 April 2005 17:04:11 [ permanent link ]
On Fri, 01 Apr 2005 07:55:30 -0500, Wayne.B <waynebatrecdotboats@hotmail.com> wrote:
On Fri, 01 Apr 2005 06:12:07 GMT, "mgg" <mike@pacbell.net> wrote:>
Assuming 10% prop slip, that's what I calculate also.>>
51 mph at 15 % , and 48 mph at 20%.<<>>
Would a SS prop reduce slip?>
=================================>
It's hard to say, but it might. The advantages of stainless over>aluminum are structural rigidity (less flex) and surface smoothness>(less friction). Improving either quality could decrease slip which>would have the effect of increasing speed at comparable RPMs.
I wonder if powder coating a aluminum prop would improve the way an aluminum prop works?
"Wayne.B" <waynebatrecdotboats@hotmail.com> wrote in message news:angq419r4aokv3h8najfku3j22rkjq4qgg@4ax.com...> It's hard to say, but it might. The advantages of stainless over> aluminum are structural rigidity (less flex) and surface smoothness> (less friction).
Are you sure? Methinks cast aluminum may be stiffer than steel, as it will break, as opposed to bending like steel.
It's hard to say, but it might. The advantages of stainless over> aluminum are structural rigidity (less flex) and surface smoothness> (less friction). Improving either quality could decrease slip which> would have the effect of increasing speed at comparable RPMs.>
Steel gets the job done with thinner blades, less interference with the water. More complex designs & pronounced cupping for a given blade thickness are possible in steel. We have used the OMC SST II props on our boats since 1986. They're powder coated steel. The polished props do look pretty!
"Short Wave Sportfishing" <emaildisguised@askme.com> wrote in message news:kkhq411ricjtnag7svmd67qhd35dba2tmn@4ax.com...>
I wonder if powder coating a aluminum prop would improve the way an> aluminum prop works?>
Later,>
Tom
Doubtful, in my opinion. The powder coating will add nothing to the rigidity of the prob and is not a smooth, polished finish.
Aluminum can be hard coat anodized, polished and the surface can approach a Rockwell hardness that is close to stainless, however the coating is only a few microns thick at best and will basically be a non-event in terms of making the bulk of the aluminum blades any stiffer.
Are you sure? Methinks cast aluminum may be stiffer than steel, as it will> break, as opposed to bending like steel.>
Just thinking out load.
Negative... the cast will flex more as well as being easier to break if struck. That's (in part) why SS props can be made with thinner blades and tend to perform better - because of the thinner blades.
On Thu, 31 Mar 2005 00:40:18 -0000, hexter@blazenet.net (gudmundur) wrote:
I currently have a 13.75 inch X 15 pitch aluminum prop on my 70 hp>Evinrude. The prop was really beat to death by it's previous owner, and>it is needing replaced. I use this boat for diving and skiing mostly, it>runs about 30 knots at present, and yanks me up out of the water quickly.> I was looking to go stainless, but they all seem to have a much higher>pitch, like 19 or more. What could I expect from say 13.25 X 21? I would>guess it would lug my motor down, and be very poor on pulling a skier up.
Correct. And never reach proper rpm. Try a 14.162 X 16.675. That should do it for you.
HaKrause wrote:> On Thu, 31 Mar 2005 00:40:18 -0000, hexter@blazenet.net (gudmundur)> wrote:>
I currently have a 13.75 inch X 15 pitch aluminum prop on my 70 hp>>Evinrude. The prop was really beat to death by it's previous owner, and>>it is needing replaced. I use this boat for diving and skiing mostly, it>>runs about 30 knots at present, and yanks me up out of the water quickly.>>I was looking to go stainless, but they all seem to have a much higher>>pitch, like 19 or more. What could I expect from say 13.25 X 21? I would>>guess it would lug my motor down, and be very poor on pulling a skier up.>
Correct. And never reach proper rpm. Try a 14.162 X 16.675. That> should do it for you.>
Nope. This is the "Harry Identity Thief" again, posting from roadrunner in Columbus, Ohio.
-- Bush and the NeoConvicts who control him are destroying the once-great United States.
"Wayne.B" <waynebatrecdotboats@hotmail.com> wrote in message news:angq419r4aokv3h8najfku3j22rkjq4qgg@4ax.com...> On Fri, 01 Apr 2005 06:12:07 GMT, "mgg" <mike@pacbell.net> wrote:>
Assuming 10% prop slip, that's what I calculate also.>>
51 mph at 15 % , and 48 mph at 20%.<<>>
Would a SS prop reduce slip?>
=================================>
It's hard to say, but it might. The advantages of stainless over> aluminum are structural rigidity (less flex) and surface smoothness> (less friction). Improving either quality could decrease slip which> would have the effect of increasing speed at comparable RPMs.>
