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10-02-2018, 01:36 PM
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#21
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Valued Technical Contributor
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 6,785
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Izzy:
Here is what little I know about gear ratios and some rules of thumb I have read about:
You pick the gear ratio that lets your prop shaft spin at about 1,000 rpm at a fast cruising speed. I believe your engine is rated at about 200 hp at 3,200 rpm. So at say a fast cruising rpm of 2,800 you need a gear ratio of 2.8:1 to get 1,000 rpm at that rpm.
Then you work propeller diameter against prop pitch to achieve a prop diameter to pitch ratio of about 1:1, ie "square". That is generally the most efficient prop to use.
Transmissions only come in certain ratios so pick the ratio closest to 2.8:1 and then select a prop diameter and pitch to give you as close as you can to a square prop.
Join boatdiesel and use their prop calculator to play with ratios and prop dimensions and to see what kind of performance you will achieve.
But the best approach is to find a good prop shop to work with to pick the right prop and transmission ratio to get this all to work right for your boat.
David
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10-02-2018, 02:08 PM
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#22
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Member
City: Port Charlotte
Vessel Name: Ships n' Giggles
Vessel Model: 78 Mainship 34 Mk1
Join Date: Sep 2018
Posts: 22
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That makes sense. The max torque is at 1700-1800 rpm 385ft lbs. wouldn’t that be where I want the motor running at max efficiency? Which would make my gear 1.7:1? So again I am by far not an expert but inquisitive. What is of most value torque or HP?
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10-02-2018, 02:38 PM
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#23
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Valued Technical Contributor
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 6,785
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Izzy:
These are general rules of thumb and you probably need to read Dave Gerr's Propeller Handbook for more explanation.
Maximum torque is only relevant when your throttle is to the wall and you are accelerating. Otherwise you pull the throttle back when you reach the speed you want to travel and you are then pulling much less hp and torque from the engine.
But I can say this, if you used a 1.7:1 transmission ratio (and I am not sure that they are available that small) then you would have to have a very small diameter prop to load the engine up at wot when the prop is turning at 1,880 rpm and that would be very inefficient.
David
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10-02-2018, 04:55 PM
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#24
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Member
City: Port Charlotte
Vessel Name: Ships n' Giggles
Vessel Model: 78 Mainship 34 Mk1
Join Date: Sep 2018
Posts: 22
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Im so unsure of my choice in gear. So here goes another question related to the gear and engine set up. What should I expect on the cruise side of the equation. My goal is to travel to Bimini and Cuba. I really want to put it on auto pilot at 10 to 12 knots or 7 or 8 knots and burn 1.5 GPH. If I really like the boat I’m going to put the 6.7 Cummins as that is the engine set up of choice.
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10-02-2018, 05:05 PM
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#25
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Guru
City: Cape May, NJ
Vessel Name: Irish Lady
Vessel Model: Monk 36
Join Date: Dec 2007
Posts: 4,964
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Izzy you might want to start a thread in the Power Systems forum section discussing your project. You will get more responses than in the Welcome Mat.
__________________
Archie
Irish Lady
1984 Monk 36 Hull #46
Currently in Cape May, NJ
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10-02-2018, 05:43 PM
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#26
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Member
City: Port Charlotte
Vessel Name: Ships n' Giggles
Vessel Model: 78 Mainship 34 Mk1
Join Date: Sep 2018
Posts: 22
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Teach me Jedi Night! Hahahah this is my first forum. I read what I can see on the internet but I’ve never joined. But everyone is friendly and I am enjoying it.
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10-02-2018, 05:56 PM
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#27
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Veteran Member
City: port charlotte
Vessel Name: ocean paradise
Vessel Model: mainship 1 210cummins
Join Date: Jan 2015
Posts: 44
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I have the same boat,220hp ZF 63 trans 1.75 to 1 with 20 X 20 prop just right
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10-02-2018, 05:57 PM
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#28
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Senior Member
Join Date: Nov 2011
Posts: 340
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sign up with boat diesel.com. Entry level membership is $25.00. Enter your boat and engine information in one of their calculators and it will calculate transmission ratios and propeller sizes for you. Also a lot of knowledgable guys on that site too.
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10-02-2018, 06:22 PM
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#29
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Guru
City: Cape May, NJ
Vessel Name: Irish Lady
Vessel Model: Monk 36
Join Date: Dec 2007
Posts: 4,964
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Easy peasy. Go to this link then click on New Thread.
http://www.trawlerforum.com/forums/s6/
Then copy and past your text from post #14 plus anything else relevant.
__________________
Archie
Irish Lady
1984 Monk 36 Hull #46
Currently in Cape May, NJ
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10-02-2018, 08:36 PM
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#30
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Guru
City: Upstate,SC
Vessel Name: Shipoopi
Vessel Model: derilic sailboat
Join Date: May 2012
Posts: 2,884
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You had me at Mainship, locked me in at project. Then you step it up and move from I-6 oiler to a V-8, I believe 2 stroke, diesel.
Yo kay, welcome.
__________________
This is my signature line. There are many like it but this one is mine.
What a pain in the transom.
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10-02-2018, 08:39 PM
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#31
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Member
City: Port Charlotte
Vessel Name: Ships n' Giggles
Vessel Model: 78 Mainship 34 Mk1
Join Date: Sep 2018
Posts: 22
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4stoke diesel
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10-02-2018, 08:40 PM
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#32
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Member
City: Port Charlotte
Vessel Name: Ships n' Giggles
Vessel Model: 78 Mainship 34 Mk1
Join Date: Sep 2018
Posts: 22
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But glad that either your as nutty as me or we are on to something here. What do you think of my little project where do you see the pitfalls
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10-02-2018, 09:14 PM
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#33
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Member
City: Port Charlotte
Vessel Name: Ships n' Giggles
Vessel Model: 78 Mainship 34 Mk1
Join Date: Sep 2018
Posts: 22
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Blue mainship what do you cruise at and what is your fuel burn with that set up. Not even trying to compare the 5.9 with the 6.5 as I know that engine is the gold standard. But trying to have an idea
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10-03-2018, 08:58 AM
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#34
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Guru
City: Upstate,SC
Vessel Name: Shipoopi
Vessel Model: derilic sailboat
Join Date: May 2012
Posts: 2,884
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Quote:
Originally Posted by Izzy Colon
4stoke diesel
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Quote:
Originally Posted by Izzy Colon
But glad that either your as nutty as me or we are on to something here. What do you think of my little project where do you see the pitfalls
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I'm diggin it.
I see no pitfalls as long as you stay ahead of things and think them through. Keep future repair and mainteance in mind.
__________________
This is my signature line. There are many like it but this one is mine.
What a pain in the transom.
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10-05-2018, 01:55 PM
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#35
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Veteran Member
City: port charlotte
Vessel Name: ocean paradise
Vessel Model: mainship 1 210cummins
Join Date: Jan 2015
Posts: 44
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Quote:
Originally Posted by Izzy Colon
Blue mainship what do you cruise at and what is your fuel burn with that set up. Not even trying to compare the 5.9 with the 6.5 as I know that engine is the gold standard. But trying to have an idea
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I cruise at 8.5 MPH 2 gal an hour 1400 RPM, fast cruise 14 MPH 8 gal an hour 2100 RPM.You have to have trim tabs to get MS1 on a plane
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10-05-2018, 07:56 PM
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#36
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Member
City: Port Charlotte
Vessel Name: Ships n' Giggles
Vessel Model: 78 Mainship 34 Mk1
Join Date: Sep 2018
Posts: 22
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Wow that’s impressive. I would love to hold out for the Cummins.
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10-05-2018, 09:27 PM
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#37
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Veteran Member
City: port charlotte
Vessel Name: ocean paradise
Vessel Model: mainship 1 210cummins
Join Date: Jan 2015
Posts: 44
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Of course the keel fairing help a lot to get cleaner water flow to the prop
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10-06-2018, 10:54 PM
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#38
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Member
City: Port Charlotte
Vessel Name: Ships n' Giggles
Vessel Model: 78 Mainship 34 Mk1
Join Date: Sep 2018
Posts: 22
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Do you have to go under any bridges in PC? I’m wondering am I going to have to loose the bridge? I know I will have an aluminum radar arch up for sale as that will not clear for sure.
I have to go under the Edgewater bridge by Cousley.
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10-07-2018, 09:57 AM
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#39
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Veteran Member
City: port charlotte
Vessel Name: ocean paradise
Vessel Model: mainship 1 210cummins
Join Date: Jan 2015
Posts: 44
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No bridges,my boats docked off of ohara and administration st.
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10-07-2018, 10:03 AM
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#40
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Guru
City: Cape May, NJ
Vessel Name: Irish Lady
Vessel Model: Monk 36
Join Date: Dec 2007
Posts: 4,964
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Quote:
Originally Posted by Izzy Colon
Do you have to go under any bridges in PC? I’m wondering am I going to have to loose the bridge? I know I will have an aluminum radar arch up for sale as that will not clear for sure.
I have to go under the Edgewater bridge by Cousley.
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That looks tight. You might want to measure that at high and low tides.
__________________
Archie
Irish Lady
1984 Monk 36 Hull #46
Currently in Cape May, NJ
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