Stainless Props on Starcrafts

[dusted_ya]

I'm looking to upgrade my 18' holiday I/O with a stainless prop and would like input from others who have done the same with this configuration. Looking to hear from current users of SS props. What pitch, diameter and model you ended up with and how you like them. I'm on the fence between a 17 pitch 4 blade and a 19 pitch 3 blade.

 

[ondarvr]

What do you see as the improvement in going to SS? I ask that because you may see no difference at all, or a slight improvement in some areas, don't expect a life changing result.

 

[Furrylittleotter]

I'm interested in learning more about re-propping myself. From what I've seen, there are 2 major factors: 1. If budget is a "concern" stop now. Re-propping is hard enough without trying to pinch pennies. 2. It can't be done "Online". Every reputable prop shop in our area offers a full line of "take it out and try it before you buy" service. Some of them are right at the marina where you can try several in a day. I truly believe there is no substitute for trying a real prop on YOUR boat in the water. There are simply too many factors otherwise. Forums are great but not for re-propping, imho.

Neil

 

[dusted_ya]

Furry, I did this on my last boat which was the 18' Super Sport with a 115hp outboard and that worked out great. The dealer sent me home with a couple of them to choose from and told me to test them out how I use the boat the most (which was with two fishing buddies and gear) I was surprised what a difference there was between two virtually identical props, one being aluminum and one being stainless was. I ended up spending the extra money for the stainless and loved it! We don't have a dealership nearby any more so was wondering what people are running for stainless props on these boats

Ondarvr, Stainless props are more efficient and the new 4 blade props are even more so. If the right one is used will give you better hole shot performance, fuel economy, top speed and lower on plane speeds.

 

[ondarvr]

Going SS does not mean there will be huge increases in either one, dialing an aluminum prop in the same way will get you very close to SS results, so if you need those last two mph, or possibly the every so slightest increase in MPG (that may never actually pay off), then go for it, but don't think there will a huge difference with either material if they've both had the same effort put in to get the performance you desire.

​The other thing is, on a hull like yours you may not see the benefits of what some SS props can offer.

​And going to a 4 blade is only more efficient in certain applications, you seem to have succumbed to a great deal of hype on this subject.

 

[Furrylittleotter]

Asking for information on a restoration forum is hardly "succumbing to hype".

I think it's common knowledge getting the exact right prop isn't easy. That being said, any knowledge helps.

Neil

 

[ondarvr]

He listed several things that a 4 blade prop "will" do, they can do those things, but you typically don't get all those benefits at one time, you need to pick which ones are important to you and work in that direction, hoping that the negatives are offset by the benefits.

 

[Old Irving]

Furry, I did this on my last boat which was the 18' Super Sport with a 115hp outboard and that worked out great. The dealer sent me home with a couple of them to choose from and told me to test them out how I use the boat the most (which was with two fishing buddies and gear) I was surprised what a difference there was between two virtually identical props, one being aluminum and one being stainless was. I ended up spending the extra money for the stainless and loved it! We don't have a dealership nearby any more so was wondering what people are running for stainless props on these boats

Ondarvr, Stainless props are more efficient and the new 4 blade props are even more so. If the right one is used will give you better hole shot performance, fuel economy, top speed and lower on plane speeds.

Dusted, what prop did you go with. I have the same set up.

 

[dusted_ya]

So I went to a boat shop near me and talked to the owner who took a look at my boat and told me that the prop I had on was 21 pitch. He asked how I used the boat, how that prop reacted and what was my WOT rpm's. He gave me the "I don't recommend stainless props unless you really know the water you are on and there are no potential hazards" speech which I agreed. He then gave me a 3 blade 15" dia. (Bigger than stock aluminum prop) 19 pitch Mercruiser Mirage to try out. I had to modify the trim tab for clearance but here are the results:

* Faster on plane times even with 3 large people in the boat
* Identical top speed
* WOT at 4300 rpm
* Cruises at 30 mph at 3500 rpm
* Quieter like the old prop was out of balance or something.
* WAY better fuel economy as GPS showed I traveled 34 miles in two day on 5.6 gallons of gas.

 

[Alumarine]

So I went to a boat shop near me and talked to the owner who took a look at my boat and told me that the prop I had on was 21 pitch. He asked how I used the boat, how that prop reacted and what was my WOT rpm's. He gave me the "I don't recommend stainless props unless you really know the water you are on and there are no potential hazards" speech which I agreed. He then gave me a 3 blade 15" dia. (Bigger than stock aluminum prop) 19 pitch Mercruiser Mirage to try out. I had to modify the trim tab for clearance but here are the results:

* Faster on plane times even with 3 large people in the boat
* Identical top speed
* WOT at 4300 rpm
* Cruises at 30 mph at 3500 rpm
* Quieter like the old prop was out of balance or something.
* WAY better fuel economy as GPS showed I traveled 34 miles in two day on 5.6 gallons of gas.

What motor?

 

[dusted_ya]

This is on a 18.5' 1970 Holiday with the 120 mercruiser I/O. Bottom end was not touched as I have about 115 psi compression on all cylinders. Top end was rebuilt with new stainless valves and hard seats for unleaded fuel. Pertronix electronic ignition. Everything else is stock.

 

[Furrylittleotter]

Did you happen to test compression after the rebuild? I've heard stories about stainless valves leaking.

Neil

 

[dusted_ya]

Compression test was done after rebuild. Never heard of stainless valves leaking and I've built many performance motors over the last 30 years. Maybe if they were installed in an old head with worn out guides.

 

[Watermann]

The reason you had to modify the trim tab is because of the newer style props rake, not the diameter. I too would suggest using a newer style 3 blade aluminum prop over the stock dog eared props that are normally found on the 120 MC.

 

[Furrylittleotter]

That's cool. Just curious. Did the compression change after rebuild?

 

[dusted_ya]

That's cool. Just curious. Did the compression change after rebuild?

Never put the boat in the water or fired up the motor prior to restoration. When I bought the boat all I checked was if the motor turned over by hand and it did. After that I took it apart to have the heads rebuilt.

 

[dusted_ya]

The reason you had to modify the trim tab is because of the newer style props rake, not the diameter. I too would suggest using a newer style 3 blade aluminum prop over the stock dog eared props that are normally found on the 120 MC.

Correct and the new props are an inch deeper than the old stock ones. I mentioned the larger diameter in the previous post so people would know that it was grabbing more than the stock one. Both pitch and diameter affect how a prop will react.

The replacement prop had these factors coming into play:
1. larger diameter grabs more water
2. less pitch but...
3. less flex and higher efficiency due to...
4. more modern design

The guy who sold me the prop said I could replace the trim tab with a performance one or just not use one at all. I spent maybe 10 minutes with a hack saw and grinder to get adequate clearances and it works great now anyways as the boat tracks perfectly straight.

 

[Watermann]

As far as brands of aluminum props I've had really good experience with the Quick Silver Black Diamond. Right now I have a QS BD 23p on my Chief with the 4.3L LX and my cruise speed is 28-30 MPH at 3k depending on conditions and trim. I found that the 40 MPH hump is tough to break over without lots of throttle and HP.

What's your top end at WOT? I would imagine that 800 RPM increase to WOT 4300 has a pretty small gain from what you're saying is a 3500 rpm 30 MPH cruise speed. For that 120 I'd think a 3k cruise would be easier on fuel and the motor.