Prop rotation on B-28

[slochner]

Is there a meaningful difference in performance if the counter rotating props on my Mercruiser powered B-28 turn towards or away from the keel? By ``towards`, I mean that the direction in forward gear on the top half of the propeller is to the centerline.

[Harry Babb]

Personally I don't think it matters......I think the performance will be the same either way.....especially on "Outdrives"/"Outboards"

But......understand this only my opinion based on my simple minded way of thinking....

Like you I am anxious to hear what the experts say.....this question has come up many times before in the years past.

For sure you must consider is that you setup so that the transmissions/outdrives are running using the clutches/gears that are indeed intended for "Forward"

hb

[slochner]

Thanks for the reply Harry; I had pulled my mecruiser 350/s months ago to fix an oil leak and replace rotten stringers and aft engine compartment bulkhead. When I put them back in the boat, I erroneously flipped them port to starboard. Am hoping that by similarly switching the props, I can avoid the time and money involved in pulling the engines back out. This would clearly result in changing the direction of the props relative to the centerline. This will maintain the proper forward/reverse gear relationship, but I do not know what impact this switch will have on handling, stability, and efficiency. Willl keep you advised.

[Navatech]

Thanks for the reply Harry; I had pulled my mecruiser 350/s months ago to fix an oil leak and replace rotten stringers and aft engine compartment bulkhead. When I put them back in the boat, I erroneously flipped them port to starboard. Am hoping that by similarly switching the props, I can avoid the time and money involved in pulling the engines back out. This would clearly result in changing the direction of the props relative to the centerline. This will maintain the proper forward/reverse gear relationship, but I do not know what impact this switch will have on handling, stability, and efficiency. Willl keep you advised.

Well, if correcting a mistake is your main concern here then I'd say that whatever advantage may exist in the original setup the effort to correct the mistake won't be worth the effort... If I were you I'd just leave things as they are... Should you need to again remove an engine that's when I would rectify the error... Seeing as half of the job is already a given due to circumstances... Just changing the props won't help you here... For one, reverse would now be forward and forward would now be reverse (the prop's design is dependent on the regular turn direction of the shaft - i.e. by putting a LH prop on a RH shaft you'd effectively be putting it in reverse)...

[mike ohlstein]

Some say that the boat will be harder to maneuver at slow speed and very difficult on one engine. Others say that the boat may ride with the nose slightly down at cruse.

I don't know about, but I can't imagine that your wake pattern is going to be exactly the same as it used to be at 1100 rpm. If you're superstitious about things being 'exactly so' when trolling, you may not be happy.

[slochner]

When I suggested switching the props, I meant switching to props port and starboard, so that the props are attached to their matched engines.

Spoke with Todd at Blair Propeller in Stuart, FL. He identified two possible effects of having the props turning towards the centerline: 1. Their combined effect may tend to raise the stern a bit, lowering the bow. He opined that if I formerly had to use my trim tabs to get the stern up at cruising speed, this might even be a benefit by reducing the need for trim tab.
2. Twin inward rotating props might be so close together as to feed off each other`s cavitation effect, thereby increasing cavitation. He did not recall this being a problem with Bertrams.

Scheduled to switch props in one week - will post any noteworthy results thereafter.

Thank you all for your consideration.

[Tony Meola]

Are the engines counter rotating or is it done through the transmissions. If it is transmission couldn't you just pull the tranny and swap them. Would be way easier, unless you can't get them out without taking out the engine.

[slochner]

Have switched props, will report results as soon as I solve engine problem (see thread entitled " Mercruiser 350 Starting Problems")

[Navatech]

FWIW, on the naval vessel I served on we had 4 shafts and 4 props... The inner props turned inward and the outer props turned outward...