Texasmark
Supreme Mariner
- Joined
- Dec 20, 2005
- Messages
- 14,795
Well, the adm guys got my login straightened out after the transition and now I'm back in and rearing to go.
This is long, but I think educational for a lot of folks; otherwise I wouldn't be "wasting my time".
For those who haven't heard of/followed my prop caper, I decided to buy yet another prop for my little boat. This time I bought a Hustler aluminum (from iboats; where else....Grin).
Hustler props are advertised on this site so you can pull up the tech data that it boasts if curious. Hard to tell it's aluminum, except for the paint. They even have a US patent number on it.
-------------------
First of all I have a 90 hp engine on a very light, fast bass boat. It has a 2.3 gearbox so it turns a higher pitched prop than most engines.
My last prop (3rd in a series) was a 13 1/2 x 24 Ballistic SS. I was suffering from what's called "clutch rattle" in that at low rpm's the shifter clutch dog in the lower unit rides back and forth on the F gear and it makes a terrible racket when in gear and at idle. (Course, give it a couple hundred more rpm's and it goes away.)
I read and heard (from the dealer) that aluminum props resisted this as they were lighter in weight which helped stop it. So, for a 100 bucks, I thought, what the heck.
Since I was running a 24P already, I didn't want to give up any performance and the Hustler advertised how performance oriented it was.
Closest I could get was a 14 1/4 x 23 and bought it, but I found out (upon receipt) that it was built for the larger Merc gearboxes and I had to improvise a shim to get it on my engine. The OD of the hub and my gear box were the same however; the prop just didn't slip down into the gearbox adapter like the regular prop did.
In the tests I ran, the two main differences were top end and cruising thrust (yeah I know, you already knew that...grin).
Top end: The large diameter grabbed more water and hence loaded my engine to the point where my WOT rpm's dropped from 5600 to 5000 and corresponding speed dropped from 50 to 44. In tight, high speed turns, trimmed out, the Ballistic would ventilate every time and rpm's would go up about 200, but it would not blow out; upon completion of the turn, in a couple of seconds it would clear out the air and drop back to 5600 (actually felt like it was ported, but it's not).
The alum however, held tight in all but one turn and when it blew it blew all the way and I had to cut the throttle. Confusing since it had done so good otherwise.
Cruising Thrust: This really surprised me. I had great control over the boat attitude all the way from plane to WOT with the Hustler. Very little slip; like 12% on plane to 6% at WOT whereas the Ballistic was running 35% at plane to 9% at WOT.
What this lack of slip did for me was give me measurable speed increases at the lower rpm's, like at 25 mph, was only turning 3000 vs 3400 and that's with a prop with 1" less pitch.
Looking at the graph from an rpm perspective, at 3000 the Ballistic was just getting the boat on plane at 18 mph and the Hustler not only had it on plane, but had it up at 25mph. Quite an impressive difference if you are a "cruising" person. This translates to MPG folks.
So in short, hands down, if I were interested in running slower, like cruising around with a big load, I would get the largest diameter prop I could and pitch accordingly. I know we talk a lot on here about doing what I just said, but I have the data and it is very true what people (in the know) say. Felt funny to be experiencing what people said about large diameter props and pushing (when tested on the same rig).
But, I'm out for the top end so I put the Ballistic back on and now have another new prop sitting on the shelf.
Hope this helps someone out there.
Mark
This is long, but I think educational for a lot of folks; otherwise I wouldn't be "wasting my time".
For those who haven't heard of/followed my prop caper, I decided to buy yet another prop for my little boat. This time I bought a Hustler aluminum (from iboats; where else....Grin).
Hustler props are advertised on this site so you can pull up the tech data that it boasts if curious. Hard to tell it's aluminum, except for the paint. They even have a US patent number on it.
-------------------
First of all I have a 90 hp engine on a very light, fast bass boat. It has a 2.3 gearbox so it turns a higher pitched prop than most engines.
My last prop (3rd in a series) was a 13 1/2 x 24 Ballistic SS. I was suffering from what's called "clutch rattle" in that at low rpm's the shifter clutch dog in the lower unit rides back and forth on the F gear and it makes a terrible racket when in gear and at idle. (Course, give it a couple hundred more rpm's and it goes away.)
I read and heard (from the dealer) that aluminum props resisted this as they were lighter in weight which helped stop it. So, for a 100 bucks, I thought, what the heck.
Since I was running a 24P already, I didn't want to give up any performance and the Hustler advertised how performance oriented it was.
Closest I could get was a 14 1/4 x 23 and bought it, but I found out (upon receipt) that it was built for the larger Merc gearboxes and I had to improvise a shim to get it on my engine. The OD of the hub and my gear box were the same however; the prop just didn't slip down into the gearbox adapter like the regular prop did.
In the tests I ran, the two main differences were top end and cruising thrust (yeah I know, you already knew that...grin).
Top end: The large diameter grabbed more water and hence loaded my engine to the point where my WOT rpm's dropped from 5600 to 5000 and corresponding speed dropped from 50 to 44. In tight, high speed turns, trimmed out, the Ballistic would ventilate every time and rpm's would go up about 200, but it would not blow out; upon completion of the turn, in a couple of seconds it would clear out the air and drop back to 5600 (actually felt like it was ported, but it's not).
The alum however, held tight in all but one turn and when it blew it blew all the way and I had to cut the throttle. Confusing since it had done so good otherwise.
Cruising Thrust: This really surprised me. I had great control over the boat attitude all the way from plane to WOT with the Hustler. Very little slip; like 12% on plane to 6% at WOT whereas the Ballistic was running 35% at plane to 9% at WOT.
What this lack of slip did for me was give me measurable speed increases at the lower rpm's, like at 25 mph, was only turning 3000 vs 3400 and that's with a prop with 1" less pitch.
Looking at the graph from an rpm perspective, at 3000 the Ballistic was just getting the boat on plane at 18 mph and the Hustler not only had it on plane, but had it up at 25mph. Quite an impressive difference if you are a "cruising" person. This translates to MPG folks.
So in short, hands down, if I were interested in running slower, like cruising around with a big load, I would get the largest diameter prop I could and pitch accordingly. I know we talk a lot on here about doing what I just said, but I have the data and it is very true what people (in the know) say. Felt funny to be experiencing what people said about large diameter props and pushing (when tested on the same rig).
But, I'm out for the top end so I put the Ballistic back on and now have another new prop sitting on the shelf.
Hope this helps someone out there.
Mark
))))