Sharrow Props

[Submariner]

REVERSING A C?
Sub...fantastic analysis...thanks. Now, for you, or anyone who knows....fuel spend is not a huge factor for us - related to how we use the boat - which is primarily day boating. I mean less fuel is better but we will not recoup ROI if we gauge it on fuel spend. I like tinkering around and improving, and I like to "feel" any changes at the helm. My "feelz" are the pay off for us.

So regarding the 5 blade - the C 24 is a sumbiiich to back up. If current is running side to - even the yammy cranked full to the side and the throttle hammered - the stern will not respond. And TBH, even with no side current, it doesn't back up well at all.

I assume this is because A: the aggressive steps work directly against reverse thrust and B: the fulcrum effect of the prop being so far back with the bracket, etc.

I got a little relief going from 3 blade to 4....and I trim engine up so that less of the thrust is bouncing off the stern....but still not good. .I would like your theories on a 5 blade in this situation.

As well as your predicted impact on mid range acceleration and hole shot. (the 4 blade + SKR have already helped this boat a lot).

Better fuel efficiency means further range between fuel docks. I'm now at 200 miles on 120 gallons of gas, going against wind and current, traveling at 30mph. This is what I was after for off-grid cruising throughout SE Alaska. (Prince Rupert to Shearwater is 204 miles. Petersburg to Sitka is 175 miles). I couldn't do either of those runs on the 4 blade prop without a fuel stop or 2 days of slow-boating at 7 knots. The 3 blade prop could do it but lacked all the other features (hole shot, reverse thrust and mid-range cruising).

I back into the current all the time with the 5 blade prop. I have more control in reverse than I do forward. I run the boat in reverse a lot. I also rarely ever use my bow thruster as I'm able to maneuver the boat just fine with the engine and a suicide knob and the 5 blade PowerTech prop. The 5 blade prop is a better fit than the 4 blade prop I ran ever was, and is way better than the factory 3 blade prop, in every way.

I also want to point out, the prop's I am specifically talking about:

• Yamaha SWS II, 15.75x15 3 blade.
• PowerTech OFS, (Offshore), 15.25x15, 4 blade.
• PowerTech SCE, (Semi-Cleaver), 14x15, 5 blade, with the exhaust tube (Channel Surfing edition).

Prop size, and blade geometry are everything. Prop testing is part science and part trial-and-error.

 

[venajeff]

If you really want to be efficient and are willing to go a little slower, you could run on the kicker. I think that is about as efficient as is possible.

 

[Submariner]

If you really want to be efficient and are willing to go a little slower, you could run on the kicker. I think that is about as efficient as is possible.

Except it's not purely efficiency I'm chasing. it's efficiency balanced with time. Time has value as well.

200 miles (Prince Rupert to Shearwater, for example)

• at 30mph is about 7 hours on 120 gallons of gas. (1 day of travel)
• at 7mph is about 29 hours on 80 gallons of gas. (3 days of travel)
• at 5mph is about 40 hours on 40 gallons of gas. (4 days of travel).

Even at $6/gal of gas, one has to ask themselves is saving 33 hours of time worth $480 savings in fuel, and worth listening to the T9.9 kicker (it's LOUD) at WOT for that much time.

Since I'm not retired, time is more important than fuel costs. Being able to run 200 miles on a tank of gas in 7 hours is pretty good, with a family of 3 on board, on a long trip.

 

[venajeff]

I was actually responding to Airborne Ranger's post, for some reason it put it as a sub to yours. I was just throwing out another option if all he was after was best mpg.

 

[Submariner]

Cudos to Submariner for all the research, coordination and testing to bring this amazing prop to Ranger Tugs Owners. My Question is has any of the RT outboard owners experimented in the other direction trying to find the most fuel efficient prop at displacement speed or what I like to call the Trawler Crawl. I imagine the factory 3 blade is a great middle ground prop, but not the best choice for 6.5 knots. Perhaps a bigger 2 blade with a weird pitch or something. Having the 5 blade Channel Surfing Edition prop for running around from fishing spot to fishing spot or cruising at higher speeds, but when you want to go low and slow on a long journey, just pull up to shallow water swap props real quick and be on your way. Perhaps Martin can come up with something, being able to maximize fuel economy at both ends of the throttle gives a Captain so much more flexibility. Maybe he will and have a Channel Surfing Prop Set for R25's and 27's. That would be awesome!

I saw slightly better fuel efficiency at slow boat speeds (5-7 knots) with the 4 and 5 blade over the 3 blade prop. The kicker, is by far, the most economical way, at 5mpg (1gph at 5mph), which is WOT for it.

You can view all the data sheets I have published, which include the 3 blade factory prop on an R25 and R27, as well as the 5 blade prop. Testing always included a slow-boat speed/gph test.

Propeller | LetsGoChannelSurfing

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