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Old 15-11-2016, 17:47   #1
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3GM30F, Morgan Out Island 28 Prop

I need prop recommendations for a recently acquired 28 Morgan Out Island.

The basic specs are as follows:

74' Morgan Out Island 28 (LWL 23.83', Beam 9.25', Displacement: 7600 lbs); Repowered with Yanmar 3GM30F (Freshwater cooled), 27HP @ 3,600 rpm; Kanzaki KM3-A Gear, Ratio 2.62:1.

The current prop is a 10 X 7.4 X 3; however, the boat tops-out at approximately 2.5 knots; and, has little or no reverse thrust.

Any assistance would be greatly appreciated. Thanks in advance!

Rick
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Old 15-11-2016, 19:37   #2
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Re: 3GM30F, Morgan Out Island 28 Prop

The 28 Morgan Out Island originally came with the Atomic A4 gasoline engine and probably had something like a 11X8 Martec propeller with a direct drive transmission (no reduction gearing). Your Yanmar 3GM30F would need a 18X9 propeller because of the reduction gear and slower turning diesel. You are going to need a propeller tip clearance to boat hull of 10% of the diameter of the propeller, or about 2". So the question is how much propeller tip clearance do you have? Otherwise you will need to lower the propeller shaft and engine bed for the larger propeller if that is even possible. What about a constant velocity universal joint on the back of the transmission so that the propeller shaft can be angled downward and give more tip clearance? Any other weird ideas like mine?
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Old 16-11-2016, 10:22   #3
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Re: 3GM30F, Morgan Out Island 28 Prop

My prop program says:

18 X 9 X 3 --- 42% efficiency
17 X 10 X 3 --- 42% eff.
16 X 11 X 3 --- 41% eff.

18 X 10 x 2 --- 44% eff.
17 X 11 X 2 --- 42% eff.
16 X 12 X 2 --- 40% eff.

DougR
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Old 16-11-2016, 10:57   #4
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Re: 3GM30F, Morgan Out Island 28 Prop

See if a direct drive transmission exists for a 3GM30 which would be an easier fix than relocating the propeller shaft so there is enough clearance between the hull and the propeller tips. By the way, two bladed propellers have the same efficiency or a little better than 3 blades. The thing with three blades is there is slightly less vibration and cavitation problems are reduced. Need to do the math on that whatever you buy.
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Old 17-11-2016, 10:08   #5
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Re: 3GM30F, Morgan Out Island 28 Prop

Go with the greater diameter possible and adjust for pitch. as DougR.
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Old 17-11-2016, 10:35   #6
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Re: 3GM30F, Morgan Out Island 28 Prop

As a guess, increase you pitch if you don't have clearance for more dia. or both if you do. Doing major boat alterations sounds like something not necessary or smart. You should have plenty of shaft HP to swing more wheel. Before altering the shaft angle, I would look at changing the reduction gear ratio.
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Old 17-11-2016, 12:18   #7
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Re: 3GM30F, Morgan Out Island 28 Prop

Think DougR has hit the nail on the head . If you can get a 2 blade 18" by 10 pitch and still have 2" between the hull and the prop tip, you'll do fine. If not, then the biggest diameter that will give you the 10% clearance and adjust the pitch according to DougR's chart. Its not worth changing the prop shaft angle. Bigger diameter will also help cure your reverse problem.l
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Old 17-11-2016, 13:41   #8
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Re: 3GM30F, Morgan Out Island 28 Prop

This is nonsense. A 13" , 3 blade prop will push that boat over 6 knots.
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Old 17-11-2016, 14:39   #9
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Re: 3GM30F, Morgan Out Island 28 Prop

Before assuming the prop you might check your RPMs, linkage, marine growth on the prop, etc. Don't laugh, after a long period of disuse my prop would not back the boat at all. Thought I lost the prop or key but it was just heavy growth. Your top of 2.5 Kts is extreme. Hard to believe that a wrong prop cuts over half your speed. Had the former owner been using it after it was repowered? If so, hard to believe he would have tolerated that performance.
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Old 17-11-2016, 14:52   #10
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Re: 3GM30F, Morgan Out Island 28 Prop

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Originally Posted by Dave22q View Post
Before assuming the prop you might check your RPMs, linkage, marine growth on the prop, etc. Don't laugh, after a long period of disuse my prop would not back the boat at all. Thought I lost the prop or key but it was just heavy growth. Your top of 2.5 Kts is extreme. Hard to believe that a wrong prop cuts over half your speed. Had the former owner been using it after it was repowered? If so, hard to believe he would have tolerated that performance.
You may have pointed out the obvious? I made the assumption that a fouled prop had been checked.
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Old 17-11-2016, 15:03   #11
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Re: 3GM30F, Morgan Out Island 28 Prop

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Originally Posted by Scaramanga F25 View Post
Go with the greater diameter possible and adjust for pitch. as DougR.
Yep, you need the tip clearance to the hull mentioned earlier. You can then use that diameter and get the pitch calculated for you. 10" diameter sounds awful small.
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Old 17-11-2016, 15:57   #12
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Re: 3GM30F, Morgan Out Island 28 Prop

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Originally Posted by Cheechako View Post
Yep, you need the tip clearance to the hull mentioned earlier. You can then use that diameter and get the pitch calculated for you. 10" diameter sounds awful small.
Yup, 10" is ridiculous small. Sound like a 10 HP OB hi thrust. And even that would push that boat 6 knots.

Put in an 18" prop?! change the shaft angle!!!!!! Ha, ha, ha, u guys kill me.
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Old 17-11-2016, 15:59   #13
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Re: 3GM30F, Morgan Out Island 28 Prop

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Originally Posted by ramblinrod View Post
Yup, 10" is ridiculous small. Sound like a 10 HP OB hi thrust. And even that would push that boat 6 knots.

Put in an 18" prop?! change the shaft angle!!!!!! Ha, ha, ha, u guys kill me.
Looking on line it's hard to find views of the prop/rudder area. But one pic looks like your prop size may be pretty limited. Small will work, you just have to get the pitch right.
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Old 17-11-2016, 22:09   #14
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Re: 3GM30F, Morgan Out Island 28 Prop

Quote:
Originally Posted by DougR View Post
My prop program says:

18 X 9 X 3 --- 42% efficiency
17 X 10 X 3 --- 42% eff.
16 X 11 X 3 --- 41% eff.

18 X 10 x 2 --- 44% eff.
17 X 11 X 2 --- 42% eff.
16 X 12 X 2 --- 40% eff.

DougR
Just curious, what is the definition of 'efficiency' in this case? Is there a 'maximum', real world efficiency that can be achieved and/or expected?

10x7x3 seems tiny, I have a 12x10x3, with an MD2020 (18hp)...
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Old 18-11-2016, 09:35   #15
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Re: 3GM30F, Morgan Out Island 28 Prop

10" seems like it must be mostly the center hub mass.
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