Propellor Slip

[bgagne]

1988 minx
383 stroker
Alpha drive
24p hydromotive QIV
Starts to slip with minimal trim at any rpm, someone had previously installed closed cooling with intake thru hull per the photo. I am thinking that the intake is causing ventilation to the prop. Any thoughts or experience with this?

[Ghost]

HMMM, how far off the keel center is the edge of that pickup? And what are the dimensions of the pickup, roughly?

[gcarter]

It's a shame someone installed that pickup. It could be removed and repaired.
I recommend a Stainless Marine pickup like this. It really has no impact on the boat
and all the water you can use. See the pic....

The Hydro Q4 is a rock solid prop on 24* Donzi hulls.
Does it have a rubber hub that might be spinning?

[gcarter]

It could also be the coupler. I just had a coupler failure that had none of the classic
characteristics of failed couplers. Once you hit about 2000-2500 RPM, it would let go.

[osur866]

It's a shame someone installed that pickup. It could be removed and repaired.
I recommend a Stainless Marine pickup like this. It really has no impact on the boat
and all the water you can use. See the pic....

The Hydro Q4 is a rock solid prop on 24* Donzi hulls.
Does it have a rubber hub that might be spinning?

Ditto, I'm running same water pick up for my intercooler works great!

[bgagne]

I will get the exact dimension, but it is about 12" from the centerline.
Prop is solid hub.
Does not slip at all until you start to trim it, at 3000 rpm if you just bump the trim button; it will slip immediately.
A couple of other interesting observations:
Previous owner tells me that the best top speed he saw with the stock 260hp was 52 mph. I am not sure of the prop or trim capability at that time.
Currently, with 375 hp, WOT with trim and slip is 5000 rpm, 62 mph, 19.8% slip.

[BUIZILLA]

probably not your problem..

BUT

Rule #1 is NEVER run a solid hub prop with an Alpha drive, ever.

if it's an SS drive what you are experiencing is the same issue I had with the same hull, and SS drive, and ANY prop I tried

I would pull the drive and check the shaft splines carefully where it rides in the coupler first, as you trim out the driveshaft slides farther out the coupler connection...

I would be surprised with a 4 blade if the pickup is an issue

or you could mount a GoPro on the transom and watch the water integrity as it leaves the transom and surrounds the drive underway

[Ghost]

probably not your problem..

BUT

Rule #1 is NEVER run a solid hub prop with an Alpha drive, ever.

if it's an SS drive what you are experiencing is the same issue I had with the same hull, and SS drive, and ANY prop I tried

I would pull the drive and check the shaft splines carefully where it rides in the coupler first, as you trim out the driveshaft slides farther out the coupler connection...

I would be surprised with a 4 blade if the pickup is an issue

or you could mount a GoPro on the transom and watch the water integrity as it leaves the transom and surrounds the drive underway

100% concur. (My next question was confirming X dimension.)

As as a side note, I'd make plans to change the water pickup regardless. I bet the one you have disturbs flow and costs 1-2 mph, where a transom pickup like George's will be much less drag. Even better just to use the one in the drive IF it's sufficient, which it may not be.

But having nothing protrude below the hull is helpful for flexibility with trailer loading, fork lifting, rack storage, etc. I had a Harry Homeowner depth sounder sticking out of my hull when I bought it and it was always a problem at the boatyard. Getting rid of that was a huge improvement.

[bgagne]

HMMM, how far off the keel center is the edge of that pickup? And what are the dimensions of the pickup, roughly?

Centerline of pickup is 12" from keel and 18" forward of the stern. It is 4" x 6"

[bgagne]

probably not your problem..

BUT

Rule #1 is NEVER run a solid hub prop with an Alpha drive, ever.

if it's an SS drive what you are experiencing is the same issue I had with the same hull, and SS drive, and ANY prop I tried

I would pull the drive and check the shaft splines carefully where it rides in the coupler first, as you trim out the driveshaft slides farther out the coupler connection...

I would be surprised with a 4 blade if the pickup is an issue

or you could mount a GoPro on the transom and watch the water integrity as it leaves the transom and surrounds the drive underway

Standard drive, not SS; I assume it to be a standard X dimension. Not ride will find a way to get a look at the water flow coming off the bottom of boat.

[bgagne]

100% concur. (My next question was confirming X dimension.)

As as a side note, I'd make plans to change the water pickup regardless. I bet the one you have disturbs flow and costs 1-2 mph, where a transom pickup like George's will be much less drag. Even better just to use the one in the drive IF it's sufficient, which it may not be.

But having nothing protrude below the hull is helpful for flexibility with trailer loading, fork lifting, rack storage, etc. I had a Harry Homeowner depth sounder sticking out of my hull when I bought it and it was always a problem at the boatyard. Getting rid of that was a huge improvement.

There is now an engine mounted water pump. If I route the water inlet back thru the drive do I use both the pump in the drive and the one on the motor or eliminate one of them? Was closed cooling available direct from merc in 1988, and if so how did they handle it? I have done numerous searches on this topic and ther appear to be a lot of different opinions.

[Morgan's Cloud]

That thing definitely has to go from the bottom ! Even if the original installer's intentions were good the thing looks much larger than it needs to be .
I don't see any reason why with a little creativity you couldn't retain the raw water pump (not to be confused with the circulating pump) and route the water pickup through the drive.

[BUIZILLA]

with your already in use crank mounted pump by all means us George's theme of water pickup..

if you can find an old flush mount transducer you can use that to plug the hole

[gcarter]

I had an '86 Minx w/transom pickup, closed cooling and an electric Mezziere
circulating pump. It was powered w/a 315-325 HP 350 It was propped w/a
15-1/2" X 22" Hydro Q4. This was the best prop I ever tried on the boat.
It would NOT blow out!
In the picture you can see the drive, pickup, and prop.
On any but the warmest days, it would go 65.

If you'd like to see more, look here:
http://www.donzi.net/forums/showthre...3-Break-s-over!

[gcarter]

There is now an engine mounted water pump. If I route the water inlet back thru the drive do I use both the pump in the drive and the one on the motor or eliminate one of them? Was closed cooling available direct from merc in 1988, and if so how did they handle it? I have done numerous searches on this topic and ther appear to be a lot of different opinions.

Eliminate the drive pump. It probably uses 2-4 HP and the water is not needed for anything. If it hasn't already been done, remove the hose between the drive and the gimbal housing. Water will continue to flow through the drive for drive cooling purposes. You'll have to get a merc block off plate for the inside of the gimbal if it hasn't been done.
Plugging the pickup hole is fairly easy. If you need help, just ask.