Quick question about prop offset

[Mark Poole ModVP]

Working on a mono, not 100% sure about which way to offset propshaft for countering prop torque. Is it to the right? (starboard)

 

[anthony_marquart]

I think that would make it worse.. you'll get more responses though.. been a long time since I ran a mono..

 

[Ray Sametz]

Mark, if it's surface drive offset to right, looking from rear. Finch suggested this on the 21 Wild Thing, the last mono I ran............==={}

 

[Mark Poole ModVP]

I saw a pic a while back of an electric mono, looked like it was offset right. But never know if you are looking at reverse image photo! Thanks.

 

[Andy Greene]

I guess it would depend on how you define offset- Are you referring to where the strut is mounted on the transom or the shaft angle exiting the boat.

On a Seaducer- X-Mono(90 boat) the strut actually angles from the transom to the left of center line (facing the rear of the hull ) by 3 degrees, the strut is constructed with the offset built in -from the mounting boss-to the shaft area.

Andy

 

[Mark Poole ModVP]

Yes Andy, where the shaft exits the transom, not an angled strut.

 

[John Finch]

If it is a seaducer use the seducer strut and rudder location as suggested by Jerry and things will work perfectly. If it is a boat with trim tabs you can have the right tab down a bit to counter torque. The shaft on most boats should exit to the right of centerline or directly in the center. Never to the left of center. The theory is that the prop lifts the hull, so if it is right of center it helps to lift the right side of the boat to counter torque roll. I always exit the shaft to the right of centerline unless running SAW. If running SAW the rudder causes lift on the right side and having both the rudder and prop lifting the right side the boat will actually lean left because the boat is litteraly flying and rudder lift is greater. It is a balance act on a mono so if you don't get it right you can adjust the rudder and strut to bring things into tune.. The more the rudder is to the right the more it lifts the right side of the hull. All this is assuming the prop shaft and strut are running straight back and not offset or steered to the right or left.

One mistake we made in the 1980s was to have the strut exit the transom in dead center of the keel and then offset or bend the strut to the left to try to steer the boat left. That put the prop to the left of the keel centerline which helped lift the left side of the boat which made chine walk absolutely horrible. Having the prop to the right of centerline reduces that chine walk. Again......it is a balance act. Chine walk and torque steer can both be totally eliminated by adjusting the strut and rudder locations.

As far as angle of the strut in relation to the bottom of the boat I always like to set the strut so it runs parallel to the keel.

 

[Mark Poole ModVP]

Thanks for the info!