prop shaft

Does anyone know what the porp shaft length is for a 79 ski nautique 351w 1:1 velvet drive 4" coupler? Trying to figure out the right length to order parts so I can fix it on the lift in a hour and not have to but it on the trailer to fix.

Midwest CC said it was a 50" shaft, what's your thoughts on double vs. single taper?

Bill you mentioned on another thread that CC shortened the distance between the back of the prop and the strut. should I take an extra 1/2" or so off of this length to improve the operation of my boat?

79...:

I recommend the double taper shaft for two reasons:

1) No more worries about pulling the shaft out of the coupling when backing down hard.
2) I believe it gives a more square fit to the coupler for better shaft coupler alignment/trueness.

Also, my '77 Martinique has quite a bit of distance between the prop and strut. I have heard that this can cuase a bit of vibration as the shaft can flex between the prop and strut. My '93 SN has only about 1" of space between prop and strut. The '77 more like 3 or 4 inches. If you shorten the shaft, make sure it does not put the prop too close the hull as this will cause other undesirable problems. What is too close? Good question, but certainly no closer than an inch and probably more clearance is better.

Keep in mind that if you go to a double taper shaft, you will need a new coupler which is not cheap. I purchased a billet aluminum coupler that set me back about $110.00. The shaft was about $170.00 (including machining costs for custom length). I purchased the parts through my local prop shop from McDurmon Distributing. You can get shafts in many different prop end styles that use either: jamb nut, nylock nut, or castle nut. I went with the nylock style.

Jameski:

I would measure my drive shaft ('77 Martinique) for you, but I am not sure how to do it with the shaft in the boat. CC should be able to give you the factory length and then you would have to decide how much to reduce the overall length to bring the prop closer to the strut. Are you running a 13RH13 prop? If so, I believe there is plenty of space between prop and hull to play with.

David F,

Thanks anyway for the offer to measure your shaft. I don't know of any way to measure it in the boat either. I am a little worried about hull clearance if I shorten my shaft. If I remember correctly, I barely had an inch (maybe 7/8"?) with my 13X12 Michigan. I can't measure now, since my prop is on the bottom of the lake. I'll put the boat on the trailer tonight and do some measuring I should be able to determine prop clearance with a tape measure using what's left of my shaft (it broke right where it started to taper - just in front of the prop).

I think I might go with the double taper shaft as well. Sounds like the benefits might outweigh the cost. Where did you buy yours... and did you do much price comparison? What kind of puller do you use to remove the coupler from the tapered shaft? My prop puller was custom made by a machine shop and it uses three bolts - I guess it wouldn't work on a coupler - since it takes four. I have another puller that accepts 2 or 3 bolts, but the center bolt is about 6 or 8 inches long... Would it fit between the shaft log packing nut and the transmission coupler?

79nautique,

Did Midwest CC say how the 50" is measured? is that tip to tip?

BC,
Yes, the prop needs only the distance to be able to put a puller behind it. However be careful that all prop bores are not the same. Take the props if you have more than one and without the key and mark the one further up the shaft you use that spot.
Also that you have at least 1/4 in on top. With the power you have you will see the performance change.

I don't know if my boat has the original strut, but I noticed that if I shorten my shaft, I will have a VERY small clearance between my prop and my hull. I've been running a 13" dia. prop with about 3/4" hull clearance at 2" behind the strut. If I run a 12" dia. prop, I will have less than 1/2" hull clearance at 1/4" behind the strut.

Here are some pics:

Bill both of my props are located within 1/8 inch of each other on the taper. I will have to measure the spacing from the strut but the 1/4 is confussing me. It sounds like you're saying that the prop can come within a 1/4 of the underside of the haul? I would think this is a little close?

Will I have the shaft on order already and it is made out of the harder material little under 200 bucks but I may have to shorten it a little but may wait til the off season to do it.

thank you kind sir

I routered the bottom enough to keep the plate level with the bottom. Doesn't need to be a huge plate, just enouh to cover the affected area. Use libreral 5200 and stainless screws.