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bgagne
06-03-2016, 05:44 PM
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
06-03-2016, 06:25 PM
HMMM, how far off the keel center is the edge of that pickup? And what are the dimensions of the pickup, roughly?

gcarter
06-03-2016, 08:27 PM
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?


http://www.donzi.net/forums/attachment.php?attachmentid=56855&stc=1&d=1277069164

gcarter
06-03-2016, 08:32 PM
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
06-03-2016, 09:53 PM
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?


http://www.donzi.net/forums/attachment.php?attachmentid=56855&stc=1&d=1277069164
Ditto, I'm running same water pick up for my intercooler works great!

bgagne
06-04-2016, 06:49 AM
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
06-04-2016, 06:56 AM
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
06-04-2016, 09:48 AM
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
06-04-2016, 02:29 PM
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
06-04-2016, 02:32 PM
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
06-04-2016, 02:36 PM
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
06-04-2016, 02:48 PM
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
06-04-2016, 02:51 PM
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
06-04-2016, 05:13 PM
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/showthread.php?36703-Break-s-over!

gcarter
06-04-2016, 05:41 PM
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.

MDonziM
06-05-2016, 09:49 AM
I don't know about alpha drives but that is the biggest water intake I have ever seen and was probably designed for a non planing hull. 4" x 6" x (2"?) is enormous, my Blackhawk drive intake on the skeg was a slot about 2" x 1/2" and that cooled a 540ci motor. For that thing to deflect water 5" over a 2+' distance seems like a certainty to me.

Pat McPherson
06-06-2016, 12:05 PM
I had a 1987 20' Minx with stock 350mag/270HP and Alpha. At WOT 4600rpm, spinning a 23p Mirage and 60 to 63mph depending on the load. Did some engine upgrades including a Tempest cam and gained 200-300rpm and 2-3mph on top.

Your boat should be running faster and that prop not blowing out...

bgagne
06-07-2016, 07:50 AM
How do I best verify the height of the drive? I cannot trim it down all of the way while on the trailer. Can anyone give me the dimension from the centerline of the bottom bolts on the transom assembly to the keel?

Pat McPherson
06-07-2016, 12:36 PM
X dimension is from drive shaft centerline to the bottom of the hull and most V bottom boats are set between 17" and 18".
I believe an Alpha drive is about 22" from prop shaft to drive shaft which would put the prop in the neighborhood of 5-1/2" below the bottom.

joseph m. hahnl
06-07-2016, 07:42 PM
Check the trailing edge of the lower unit hub . Any raised bur on the hub will cavitate the prop. Check the prop thrust washer and make sure the taper is not worn and rubbing the prop on the lower's hub and the washer on the bearing cap.

bgagne
06-12-2016, 10:24 PM
No apparent turbulelence coming from water intake.
Watching the water coming off of drive and prop it does not appear to be slipping at the prop.
It does feel more like the coupler.
After several runs messing with the trim and watching the water coming off of the transom, I accelerated to approximately 4000 rpm with the drive trimmed all of the wY down and could feel slipping, a couple of hours later, while heading back to launch ramp, there was no apparent slipping
Pulled the drive, no apparent wear on the drive shaft or in the female spline inside the coupler.

Going to just get the coupler changed ang eliminate it as a potential problem.

Ralph Savarese
07-02-2016, 10:46 AM
If the coupler was bad you would have a definite burning rubber smell from inside the engine compartment

gcarter
07-02-2016, 04:20 PM
If the coupler was bad you would have a definite burning rubber smell from inside the engine compartment

Not always, but usually.
I just changed one on the TR that didn't smell, no smoke, and physically looked fine when I removed it.
A suggestion on the Minx, after loosing a coupler on my Minx, I chose to replace the Alpha coupler w/a
Bravo coupler as they are significantly stronger. You may have to replace the flywheel cover w/one w/a larger center hole for clearance.

bgagne
07-03-2016, 10:01 AM
Waiting to get it back from mechanic. I have been out of town a lot and no time to work on it. I had someone pull engine. He said that the coupler appears to be bad. I have not had a chance to see it. Things will slow down with travel in a couple of weeks, should have it back together by then. Will update with the results.