Volvo MD7B in Bahama

[John Taylor]

Greetings all. I have question. Let's say you design and build a sailboat ike the Bahama for a MD7A engine. Let's also say that somone replaces this engine with a MD7B which has reverse rotation. How will this reverse rotation affect the handling of the boat under power? My background is airplanes and I know that the vertical fin and rudder of an airplane is rigged for the prop to turn clockwise as viewed from the cockpit. If you were to install an engine with reverse rotation it would adversley affect the yaw of the plane. Does this hold true for boats as well? My Bahama has the MD7B and when, under power, I let the wheel go the boat makes and immediate turn to starboard. I've had a diver look at the rudder and he found nothing, I've pulled the boat out of the water and the yard found nothing, I've been in touch with the very nice people at Edson Marine and they can't figure it out. So, I'm throwing this out for all you other Islander people.
Best,
John

 

[Ross]

I can only relate my experience with my Islander 30 1968 model full keel aperature for the prop. I designed the steering to be fairly tight and I can leave the wheel and go below for a cup of tea from a thermos and go back on deck and not be 10 degrees off course. The old Atomic 30 turned a RH 13x7 two blade prop and I changed to a 13x13 RH three blade prop with a 3:1 reduction gear.

Have you checked rudder position while underway on a straight course? Does your wheel also move when you turn loose? I have heard of boats that had an alignment problem with the keel. At what rate does the boat turn?

 

[John Taylor]

The boat makes an immediate right hand turn. The wheel isn't hard to hold to keep the boat on the straight and narrow but you do have to hold it. I don't know how to detect an alignment problem with the keel. It went throguh a survey, both in and out of the water, last year when I bought it and it passed with flying colors. The kind of problems that turned up on the survey were very minor. The surveyor said he'd seldom seen a boat as clean and as well cared for as this one.

 

[guest]

MDAB Rotation

I have an Islander 30 with MD7A. The only difference rotation should make is the direction of prop-walk especially in reverse. If you let the wheel go on the 30, the propwash will catch the leading portion of the rudder and push it so that the boat turns. In my case the boat does an immediate Port turn.

Greetings all. I have question. Let's say you design and build a sailboat ike the Bahama for a MD7A engine. Let's also say that somone replaces this engine with a MD7B which has reverse rotation. How will this reverse rotation affect the handling of the boat under power? My background is airplanes and I know that the vertical fin and rudder of an airplane is rigged for the prop to turn clockwise as viewed from the cockpit. If you were to install an engine with reverse rotation it would adversley affect the yaw of the plane. Does this hold true for boats as well? My Bahama has the MD7B and when, under power, I let the wheel go the boat makes and immediate turn to starboard. I've had a diver look at the rudder and he found nothing, I've pulled the boat out of the water and the yard found nothing, I've been in touch with the very nice people at Edson Marine and they can't figure it out. So, I'm throwing this out for all you other Islander people.
Best,
John

 

[John Taylor]

Thanks. As long as it's normal and to be expected I'm going to stop worrying and move on to other things. Thanks again.

 

[linz1]

I have a Bahama 30 with an MD7B and it does the same thing. I get around it by giving it a short burst of throttle which seems to override the strong starboard prop walk and allows me to go in reverse without the pull.