Screw crazy....

[bayoucat58]

I understand why twin engine boats have counter rotation to prevent listing better handling and all, But what is the real difference between in board vs. out board rotation when setting up a small say thirty foot vessel. Please enlighten me "Cat"

 

[mrcrabs]

Re: Screw crazy....

But what is the real difference between in board vs. out board rotation when setting up a small say thirty foot vessel

do you mean is there a difference between counter rotation on a inboard vs a outboard? other than the way the trim works I say theres not much but I don't really know... I think your in the wrong forum...this is other outboards and were not even sure what a prop nut is yet....I say its some one who collects props others have different opinions

 

[sasto]

Re: Screw crazy....

Much better handling with counter rotating engines and props. Some Mfg's even counter rotate props on the same shaft on an outdrive. Normally with duel engines the props rotate outboard.

(do I make any sence?)

 

[bayoucat58]

Re: Screw crazy....

Much better handling with counter rotating engines and props. Some Mfg's even counter rotate props on the same shaft on an outdrive. Normally with duel engines the props rotate outboard.

(do I make any sence?)

Hi Sasto, yes you make since so in your opinion whether they rotate in board or they rotate out board makes NO difference so long as they are countered. OK Thanks for hitting me up with that information Bonn Voyage!!!

 

[sasto]

Re: Screw crazy....

Hi Sasto, yes you make since so in your opinion whether they rotate in board or they rotate out board makes NO difference so long as they are countered. OK Thanks for hitting me up with that information Bonn Voyage!!!

Rotating outboard is the ideal way for the manufacturer. That said....I have a friend that changed his Donzi and rotated his inboard on a speed boat and swears he picked up a couple more MPH.

 

[bayoucat58]

Re: Screw crazy....

I have heard that as well. I have worked in the oil field all of my life and on every tug, supply vessel seismic vessel 90% ranging from 5000 H.P. - 1200 H.P. have always turned in board i will do more research on this and contact some old salts for there opinions and again this is a small cruise type of application. But if one will save me fuel and not slouch on performance then that's a done deal. Thank you all for your helping me understand this issue..... Cat

 

[mrcrabs]

Re: Screw crazy....

the heavy push boats use kort nozzels on them to maximize efficacy of the counter rotating wheels, there used to be alot of enrgy was wasted and showed up as huge wakes behind the 4000 hp - 8000 hp push boats, with the advent of the kort nozzel that changed dramaticaly, more thrust/fuel efficiency = better use of that power ( I know I was there ) but fo a 30 footer the science is not the same, best guess would be a duoprop setup or twin 4 cyclinder diesels for good thrust and fuel efficacy or what I prefer would be something like twin 50hp 4 cycle hondas... no counter rotation and I would just use the trim tabs to steady them since I wouldn't be looking for speed just milage and low sound.




http://www.submarineboat.com/kort_nozzles.htm

 

[nwcove]

Re: Screw crazy....

even on small boats, with a surfacing prop, "prop walk" can be an issue. counter rotation on dual motors is the way to go. having to oversteer in one direction to compensate, has to have an impact on overall performance. ( but im a newbie....so i dont know much)