89 SN prop advise (not wakeboarding)

Hi guys,

Just after some advise on the best prop for my situation. Currently running an acme 470 which suited out wakeboarding needs, but after having kids our boats getting used mostly to chug along slowly (15-20 mph) towing them around.

We've found the 470 does the job fine but want to lower the rpm at these slower speeds. Currently the engine sits on 2500rpm at 20mph and at 16/17 mph it's doing 2200rpm.

Is there a 4 blade prop that could help me out? I'd like the rpm to be at about 2000 or under. Top speed is not important nor is catering for ballast. The boat mostly only has mum dad and 2 kids so it's far from at capacity.

Thanks in advance,
Justin

There is an old post (from 2009) with Mark and others discussing the various prop options...including the 470 and the 1442
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=12704&title=new-prop-for-1989-ski-nautique

My 89 with a 422 is about 1:1 revs to mph at 30mph also. At boarding speeds 21-22mph it is about 2400rpm

I have just installed a 422 on my 1989 2001 over the weekend but time was against me with regards to getting the boat back on the water (still winterised) to do any testing
The reason I went for the 422 was as a good option for running some ballast (maybe up to 1000lbs) but also to improve the holeshot and hopefully improve the speed holding around the corners.
The 422 is replacing my old OJ Legend 3 blade which will go off for a repair and become my spare.

Bri892001 wrote: Check out this page: http://www.acmemarine.com/prop-list_ski-boat.php I believe 12.5 diameter might be on the small side as far as diameter for a full sized Nautque. A little more pitch and/or a little more diameter should bring your RPMs down. Not sure how the 4 vs. 3 blade thing will interact exactly as far as RPMs.

Most CC direct drives from 2001-2009 came with 12.5" diameter props... the 422 being the most common. Great prop, and one of the best all around options for an '89 SN.

The # of blades will have little effect on how many RPM's a prop turns. That is most closely related to pitch, though cup and diameter do have some effect. The fewer blades a prop has, the more efficient it will be, so 3-blades tend to be a little faster on top than the 4's.

I would not expect to cut 400+ RPM at any given speed unless youre considering making an extreme prop change. Doing so will drastically impact your holeshot and top end. The 422 should run pretty close to 1:1 (speed vs. RPM) on the 2001 hull with the 1.23 trans, but it goes without saying that the boat needs to be fully planed off and cruising to fall into that range. Lower speeds (20mph is right on the edge) will run higher RPM vs. speed.

Thanks fellas.

Mark, I'd love to try that 422 mate, before I splurge on a new one.

I've had this 470 repaired once and I know the po had repaired it also. Perhaps during the repairing process some cup was taken out of it. We both used the same guy who works out of his garage.

So, what rpm is the 422 running at boarding speeds mark?

Justin 21-22mph was close to 2400rpm depending on how much weight you have in the boat.(i.e 2300rpm min load to 2500rpm loaded)

Should have the 422 back latter this week. I do not plan not use it again this season as we still have a bit of debris in our waters. I could send it down to you but would like to get it back before Easter as we plan to spend the holidays camping and skiing before the season ends. (Just in case we damage the current prop over that period)

I could also send it down after Easter if that suits you better without any tight return time restraints. It only cost $22.05 to Express Post it to Austral is Sydney. It should be the same or less to and from the Central Coast area.

I have taken the hammer to my 422 numerous times over the last few years. It was due for a full checkout. I investigated my local prop repairer, he operates out of a shed and does outboard repairs. I did not think his methods were likely to get it much better than I could.
The last hit was in the middle of the blade. Previously it had just dog eared over on the tips which was reasonably easy to get back into shape without to much persuasion. I decided to send it to Austral Propeller Company as they have all the jig tools and scanning gear to get it right.