How to Spin Them
 

I am looking at a 1990 38 Top Gun with 900s and six drives,I have always been told that for straight bottoms you turn the props outward for bow lift and for step bottoms you turn the props inward for ass lift. My question is what is the real story? The owner turns them inward and gets plenty of bow lift but it doesn't hadle as well around the docks, so does it change speed on the boat one way or another? Thanks for the help.

Spinning inward will give you a few mph more, but might cause your boat (flat bottom gun) to porpoise. Spinning 4 blades in will give you bow lift and 5 blades will give you stern lift. ive never really noticed the difference around the docks as some guys claim. My boats attitude was always a bit better spinning outwards. Ive swapped rotation many times and i guess its personal preference.

IN=Bow Lift. OUT=Stern lift.

In is usually a tad faster, but sometimes reversing around the docks and what not can be tricky.

x2

This is the boat I was referring to when I asked the question and he is spinning 4 blades. http://www.offshoreonly.com/classifi...o44938-en.html

MILD THUNDER and Griff,

You guys have definitely been paying attention over the years.......
5-6 years ago, it was uncommon for anyone to answer this question on here. What a great tool this thread has become.

However, rules of thumb are made to be broken. Not the basic physics, but definitely from a seat of the pants preference side.

Nice job guys!

Brett

I know I'm very impressed and thank everyone for thier answers to my question.

Thanks Brett !

maybe the ONLY thread without bashing or insults...let's keep it that way...:evilb:

Why is it tricky around the docks when props are turning inward? Debating trying on my boss 302.

Mine spinds outwards (34 baja, no steps), and am going to try them inward soon.

Reverse seems to have less effect....trimming the
drives positive helps a bit, but it's not as good as spinning out

bigfarmer,


I Love your AVATAR pic! don't know why but it brings back old testing fly by brain pics to mind!!!!


kragar, thrust is less related to the transom when rotating inward.

JT, yes positive trim will direct the thrust below the transom....................

Brett

With props spinning outboard, when you oppose the engines to pivot, the prop-walk combines with the moment created by the thrust. I.e., you put the stbd in forward and the port in reverse, both props are spinning to starboard, which causes both props to walk to stbd, and the torque is twisting you to starboard also.

When you rotate in, the effects oppose each other. With the relatively small diameter props, with comparatively deep immersion we use, the prop walk effect is small.

I am spinning my Mercury Racing 4-blade cleavers inboard, and it pivots just fine. It probably pivots slower than it would going outboard, but who cares, I dock only once or twice per outing, and my previous boat was a single, so any additional maneuverability is just a bonus.

The boat will porpoise in the 60mph range, but you can stop it with the tabs. If I was set up to spend a lot of time running in the 60's, I'd probably consider turning them out. If you have the power, and are going to spend most of your time at higher speeds where you need the bow lift, turn them in.

coooooorect, mine spin inward on my flat bottom tiger, rotates slower but as you said doesn't matter (to me). it also matters if you have a side by side or a staggered set up..not impossible, just different.

I'm going to try spinning my hydromotives in one I get my engines back in my Formula. Spinning out, my boat ran very flat so if I can gain a little bow lift by spinning in would be nice.