Stainless 21 or aluminum 20

[Jason89sunbird]

1) Performance issue you are trying to correct.

Fastest plane speed. Bought boat from my parents with michigan aluminum 18" 4 blade prop. Planed in over 10 secs (I quit counting, annoyed) I felt it when it had volvo 19" 3 blade and it was worse. When they bought the boat it was 5yrs old and had under 60 hrs. It would get to 50 mph in calm to mild chop. Just took forever to plan.

After reading Craze1Cars post http://forums.iboats.com/non-repair...-adding-4bbl-5-0l-volvo-gl-vortec-396275.html I installed carb and spacer it helped my plane but not enough. My deep hull boat wouldn't plane nicely.

I installed nauticus SX smart tabs, boat planed in under 3 secs. Best thing I have ever did to boat.

2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch

Installed a friend's 14.5 x 21 4 blade aluminum. Planed in under 5 secs

4) Wide open throttle RPM and speed with an average load (very helpful)

4400 rpm 52mph in about 6" chop

5) Engine/drive make, model, year, and HP

Volvo 5.0 GL 2003 220hp
Mods, 4 bbl marine 4175, 3/4 inch wood 4 hole spacer, total timing 32 degrees, iridium plugs, Taylor plug wires, new BWD dist cap and rotor.

6) Boat make model, year, length and weight

2003 reinelle 200 LSE 19' 7" 2850lbs empty. So 3500lbs on the water.

My question is will the stainless be worth the money. 21 aluminum gets 4400 rpm, can the stainless plane faster and get more rpm or should I go with a 20 aluminum because I'm cheap lol

 

[Radarman68]

Re: Stainless 21 or aluminum 20

deleted.

 

[Radarman68]

Re: Stainless 21 or aluminum 20

there are far more experienced folks than I, but I think you are going the wrong way. If you go with the 20", your WOT will drop approximately 200 RPM.. if you currently have an 18" prop that would net you 4400 rpm 52mph, and is slow to plane, I suspect you are over propped. if you drop 2" pitch you would be much closer to your maximum WOT and it would plane FAR faster. My suggestion, for what it is worth, would be to 16" prop, which would ideally increase your WOT to around 4800 RPM and would be a /lot/ more snappy out of the hole.

 

[Jason89sunbird]

Re: Stainless 21 or aluminum 20

I was telling the whole story of this summer with the boat and the mods done. It now planes in under 5 secs with a 21" 4 blade. Sorry for the confusion.

 

[Radarman68]

Re: Stainless 21 or aluminum 20

so re reading your post, I see I got it a bit off. I thought you were running the 18 iwth the posted WOT numbers.. sorry.

so, on edit, "michigan aluminum 18" 4 blade prop. Planed in over 10 secs" and "volvo 19" 3 blade and it was worse" and last "14.5 x 21 4 blade aluminum. Planed in under 5 secs, 4400 rpm 52mph"

based on those numbers, it sounds like your 21" prop has much less cup that the other two which would account for the difference between the three. I think I will step back and let folks respond because when prop design comes in like this, I am out of my element.

 

[Jason89sunbird]

Re: Stainless 21 or aluminum 20

It only did that because of the smart tabs. The 18 inch planed under 3 secs, cruise speed was about 24-26 mph at 3000 rpm and top speed of 45mph at 5200rpm. If you do the math that prop sucked lol

 

[craze1cars]

Re: Stainless 21 or aluminum 20

Wow that's an old hot-rodding thread of mine...amazing it's still being dug up and used on occasion. Since then I repowered the boat to a 5.7L, and then sold it LOL...

Anyway, I see a quick and easy answer here...if you're getting 4400 rpm out of a 21 pitch 4 blade aluminum, then you'll probably be happy if you buy a 19 pitch 4 blade of similar design/brand, probably with good aggressive cup/rake. Aluminum or Stainless your choice. I have grown partial to Solas. One of those should put you right near 4800 or so, and that should give you real good holeshot and comparable to speed.

Stainless will perform a little better than alum, so if you can pony it up, buy stainless.

I think the biggest problem with how you're assessing things is the fact that you're using pitch only to make your determination. Prop design and attributes make a big difference also. Sharing actual brands/models of props you have tried would be valuable info.