22' Islander 3.0 3 vs 4 blade

I have found some very interesting reading on this forum about 3 vs 4 blade propellors. I have a 1983 Islander alum. hull with a 3.0 140 hp. The current 14.25 X19 pitch gets me 34mph at 44/4500 rpm and typical cruise speed of 22-24 mph at 32/3300 rpm. I have no complaints about the performance however i am wondering if I could save some fuel and wear and tear on the engine by switching to a 4 blade prop. I am reading about lower rpm to get on plane, better hole shot, not that I need that but would get up more quickly and save some fuel mabey. Mostly fish and cruise with the wife and grandkids. Only ocassionally do I pull the kids on a tube so performance is not an issue. I have seen the formulas used to make some of these calculations and most is greek to me. So....would it be worth my while and expense to move to a 4 blade prop to perhaps save some fuel? Thanks in advance for all your input on this great forum.

Airshot

Re: 22' Islander 3.0 3 vs 4 blade

Did you check the post below," islander 191".I think its made to order for you.
They had some really good results.A little smaller than yours but about as close as you might find.We'll be glad to help with any questions.

Re: 22' Islander 3.0 3 vs 4 blade

steelespike said:

Did you check the post below," islander 191".I think its made to order for you.
They had some really good results.A little smaller than yours but about as close as you might find.We'll be glad to help with any questions.

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While I have been thinking about this for some time, that posting is what got me to post my own. While his performance improved what about fuel economy? I also see there are a number of different 4 blade props I would assume having to do with rake angles etc. How does one go about understanding which one would be the best choice with fuel economy being a priority on the list? Perhaps I should ask for a recomendation rather than try to sort this stuff out. It sounds to me as though there are persons much better versed at this than I am.
Alpha One outdrive 1.98 gear ratio, current prop is a 14.25 X 19p, any recomendations will be appreciated.

Airshot

Re: 22' Islander 3.0 3 vs 4 blade

If you have a 3.0l 181cui why would you ever worry about fuel economy mine does close to 50mph with 3 blade 17 P and I bought 4 blade as spare pushing 19.5 ' boat . Fill up before I go and put 18-20 dollars after weekend running ? Friend just bought Nordic and runs Ohio river 72mph 48gal tanks don't matter as long as he gets to Island first .

Re: 22' Islander 3.0 3 vs 4 blade

jimbo_jwc said:

If you have a 3.0l 181cui why would you ever worry about fuel economy mine does close to 50mph with 3 blade 17 P and I bought 4 blade as spare pushing 19.5 ' boat . Fill up before I go and put 18-20 dollars after weekend running ? Friend just bought Nordic and runs Ohio river 72mph 48gal tanks don't matter as long as he gets to Island first .

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If your running a 3.0 close to 50 isn't possible with a 17" prop. In fact youy would probably be over reving if you could reach 40.
If you could do 49 you would be turning almost 6800 rpm I have a feeling your speedo may be off.

Re: 22' Islander 3.0 3 vs 4 blade

airshot said:

While I have been thinking about this for some time, that posting is what got me to post my own. While his performance improved what about fuel economy? I also see there are a number of different 4 blade props I would assume having to do with rake angles etc. How does one go about understanding which one would be the best choice with fuel economy being a priority on the list? Perhaps I should ask for a recomendation rather than try to sort this stuff out. It sounds to me as though there are persons much better versed at this than I am.
Alpha One outdrive 1.98 gear ratio, current prop is a 14.25 X 19p, any recomendations will be appreciated.

Airshot

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I don't remember the details of his progress;but boat economy can be fairly obvious and elusive as well.
At wot a motor will use fuel at a rate of 10% of the rated hp. A 140 hp about 14 gallons per hour.
That's regardless if a runabout or a house boat. The resulting speed determines actual mpg.
Of course reduced throttle produces better gph but what combination of gph and speed produces best mpg.
If a boat planes easier stays on plane better at reduced throttle responds better to a load it will likely be getting better mpg.
However best practical cruising speed could be just on plane to about 1000 rpm higher.
The difference between a good setup and a perfect setup would probably be measured in tenths.
Weight placement in the boat can change mpg. There are props that produce excellent slip numbers.
Many times a heavier glass boat will get better speed than a similar lighter al boat do to the more efficient bottom.
A ss prop usually will perform better than an al prop but again probably measured tenths or hundreds of a gallon.
Probably not worth the price.
From your concern about fuel use I think a flow meter would be a good investment . Some will do mpg on the spot.

Re: 22' Islander 3.0 3 vs 4 blade

Supreme Mariner, thanks for all that info, have already done all that stuff as I have been a boater for more than 45 yrs. I have already figured out the optimum cruising speed for best fuel economy, my intent in my question is can this fuel economy be improved noticably
by going to a 4 blade prop? Perhaps it would allow a slight reduction in rpm to maintain the same cruising speed or perhaps it would give me a greater speed at the same rpm. Then again could my fuel economy improve with less rpm and a better get on plane speed? All these articles have just got me to thinking whether it would be a good investment in the 4 blade prop. The prop engineering discussions going on about slip and performance and efficiency is not making alot of sense to me so I was hoping that someone would chime in and say that I am wasting my time, not worth the investment.....or you need this prop and you will achieve what you are looking to gain. Thanks

Airshot

Re: 22' Islander 3.0 3 vs 4 blade

Well as I suggested the difference between a good setup and an excellent setup could be hard to measure.
The 4 blade is touted to improve low to midrange performance with a slight reduction of top end.
As I'm sure you have read.
Don't forget there are reports a 4 blade has smoother operation and better control on plane and at the dock.

Re: 22' Islander 3.0 3 vs 4 blade

Yes these are all the things that started me thinking about the 4 blade prop. I guess my next concern is ...do you just order a 4 blade with an inch ess pitch or is there more to it regarding "which" 4 blade prop works best on your type of boat. I see alot of 4 blades props but most have different features among them such as rake and a bunch of other terms of which I am not sure I fully understand. Was hoping someone might chime in and say I put such and such on an Islander and it provided this type of improvement, or be sure you don't get this type of prop as it is not designed for your type of boat. When looking at 4 blade props it can be overwhelming with all that is availiable.

Airshot

Re: 22' Islander 3.0 3 vs 4 blade

I think you are over thinking this problem. hwsiii really knows his stuff unfortunately he doesn't come around any more.
You have a very close example in the Islander191, a prop guy that was second to none in your type of setup.
the Solas props have a very good reputation both for excellent results and predictability.
The Solas Amita and Rubex are the same but the Rubex has a removable hub.
It seems to me that the Islander 191 results are close to amazing with the smart tabs and Solas prop.
By the way it appears the Rubex version is slightly less than the Amita because it includes the install kit.
If you do decide on the smart tabs keep in mind apply only just enough pressure to get the improvement.
Less is more.

Re: 22' Islander 3.0 3 vs 4 blade

Thanks for the info, the Solas props are what I have been considering as they get the most plus reviews. The way my boat is loaded getting up on plane has never been an issue so I have not thought about the trim tabs, however you now have me doing more thinking.
I was only hoping for more detailed information before ordering a prop, sort of a confidence builder thing if you know what I mean. I have had boats all my life, raised on Lake Erie and thought I knew alot, but this forum here on I-Boats has certainly showed me how much I really do not know. I will probably do a little more "confidence" searching before ordering a 4 blade, but thanks for all your help.

Airshot

Re: 22' Islander 3.0 3 vs 4 blade

If you get a prop and its not quite right you should be able to sell it and move on to another at nominal cost.
If you look around you might find a dealer that will let you test drive some props with the understanding your buying.

Re: 22' Islander 3.0 3 vs 4 blade

steelespike said:

If your running a 3.0 close to 50 isn't possible with a 17" prop. In fact youy would probably be over reving if you could reach 40.
If you could do 49 you would be turning almost 6800 rpm I have a feeling your speedo may be off.

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48-78118-17 Prop
Drive Unit OB313453 don't know gear ratio for prop speed cal with slip ?
MCM 3.0Liter Rated 130Hp ser B456918
I could be wrong but after running My old Boat 18' Woodson dual cathedral w/120hp chyrlser with new 130hp power head . My new old boat is a lot faster and more fuel stingy .

Have been challenged on this a few times I guess I'll have to do a post with video of Garmin while running WOT. It's a light day cruiser 196 variable deadrise back, 3step pads running full length . Bought a 4 blade in Mercruiser box as a spare $100.00 for more grip on fast rivers and climbing waves . I got took it was a Solars when I untaped . I am pretty sure I could run a 19P as it will exceed 5000rpm.

The secret behind the remarkable performance of Moesly’s new design was its variable deadrise, longitudinal stepped V hull—a design with such phenomenal hydrodynamic features that it is still revered by naval architects today. The length of the hull was divided into three distinct planing surfaces, each with a different angle of attack and slightly recessed as they moved away from the centerline. All three planing surfaces remain in contact with the water, whether the hull’s at rest or moving slowly, providing stability. As the boat gains speed, the hull rises, freeing each successive surface until only the center running surface is wetted. With less wetted surface, the boat travels faster and with substantially less power, creating a substantial gain in fuel economy. And the other benefit is its superior rough-water performance. As the hull comes off a wave, air is trapped in the recessed longitudinal strakes, cushioning re-entry and dramatically reducing the pounding associated with other hull designs. An exceptional hull design, it remains one of the best ever invented.

Re: 22' Islander 3.0 3 vs 4 blade

Regardless of the boats configuration a 3.0 with a 2.00 gear ratio and a 17" prop with a reasonable slip of 10%
the motor would be turning 6764 rpm @ 49 mph.if you use 1%slip (impossible)it would be turning 6149.
Your maximum rated rpm is probably 4800.
Physically impossible. Perhaps you are running down stream in a 10 mph current.
Your saying your using $20 worth of gas on a weekend that about 7 gallons at $3 a gallon.
A 130 will use about 13 gallons per hour at wide open throttle regardless if pushing a house boat or a runabout.
half throttle about about 7 gallons per hour.

Re: 22' Islander 3.0 3 vs 4 blade

steelespike said:

Regardless of the boats configuration a 3.0 with a 2.00 gear ratio and a 17" prop with a reasonable slip of 10%
the motor would be turning 6764 rpm @ 49 mph.if you use 1%slip (impossible)it would be turning 6149.
Your maximum rated rpm is probably 4800.
Physically impossible. Perhaps you are running down stream in a 10 mph current.
Your saying your using $20 worth of gas on a weekend that about 7 gallons at $3 a gallon.
A 130 will use about 13 gallons per hour at wide open throttle regardless if pushing a house boat or a runabout.
half throttle about about 7 gallons per hour.

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Boat ,Fish ,GPS .8m scale also I exaggerate a lot . 24" polycarbonate plastic .Will get GPS MPH video .water pick up tube speedo , tach works on 750 rpm idle 600 in gear .Ran back to launch fuel dock and back to cove campground Friend paid for gas as was cheap .I forgot to fill when got home local gas for total so I added 5 gals and it filled . so about 40$ total



With less wetted surface, the boat travels faster and with substantially less power, creating a substantial gain in fuel economy. I bought what I thought was a 4 blade mercruiser and got home and it was The Solas For same reason hes looking Loaded boat ,Lake Erie winds ,waves , better grip and I'll try to get numbers off of when I get home but i haven't tried yet.