Best prop for an APLHA SS...SternJack install

[Lenny]

OK, since I was going to try this thing in my pursuit for the best prop for the SS I thought I would document it. Start at a baseline, same location, weather, weight etc. My goal is good handling, low transom, HIGH bow height ability, low slip. :rolleyes:

I chose a small (tiny) Lake nearby. (Elk Lake) http://www.explorevancouverisland.com/images/Observatory/Dominion_Observatory_2.jpg That is the ocean in the background. WOT runs are over in about 45 seconds. :eek: Anyways here are the specifics. This is the site I used for slip calculations. http://www.mercuryracing.com/propellers/propslipcalculator.php

-18LE 398 hours, stock 350 MAG '87, Alpha SS out back.
-Two props, a Merc 23" labbed Cleaver and a Turbo TXP 23 SS
-2/3 a tank of fuel on board (226 pounds)
-Two people for a total weight of 370 pounds
-10 Kokanee's (beer) in a bag in the bilge. (Still there too ;) ) 8 pounds
-50 pound tool box in front of my feet (to the left of me in the ski locker but close as possible to me. Aft)

So, about 650 pounds of "baggage" and a FLAT CALM DAY. Extremely wet hull, NO wind period. I trimmed the boat and took these numbers as an average after a pass in each direction on the Lake after trimming up till it slowed down in each props case. Here are the numbers.

Labbed three blade Cleaver 23"

2000 RPMS-13.8 GPS-52% slip
2500 RPMS-26.1 GPS-26% slip
3000 RPMS-30.1 GPS-31% slip
3500 RPMS-40.1 GPS-21% slip
4000 RPMS-44.2 GPS-24% slip
4500 RPMS-55.1 GPS-16% slip
4950 RPMS-59.8 GPS-17% slip WOT with this prop.

23" Turbo TXP

2000 RPMS-20 GPS- 31% slip
2500 RPMS-29.1 GPS- 20% slip
3000 RPMS-38 GPS- 13% slip
3500 RPMS-48 GPS- 6% slip
4000 RPMS-53.4 GPS- 8% slip
4100 RPMS was WOT and it was so close to above I didn't bother. It was a struggle for this motor.

The Cleaver, while higher slip but much higher RPMS was a hands down favorite. Hooked up well in the water, no blowout in turns, kept the transom low (ish) Provides negligable bow lift with trim but some. Not enough bow lift for me. Very stable prop. I would love a 25-27 of these or a 4 blade Cleaver and 150 more ponies/torque and see what it can really do.

The TXP is very unstable at WOT and tends to hook on decelleration. Very flighty at WOT, chine walks, kinda like riding a horse at speed. No blowout and corners phenomonly. Midrange (3500) is incredible. Transom runs FAAARRRR to high. It is visibly way higher which I imagine contributes to the poor WOT handling.

Next, same tests, same place, same weight, same weather and this thing now hangs off the back. This weekends chore. :)

Let's see if I can't create some serious bow lift with this new "thing" and still keep the Cleaver hooked up. If I can, then a pile of goodies go into this motor or another. :D

[BUIZILLA]

the front seat passenger is costing you 6 mph right off the bat with that drive....

he/she/they/whatever should have sat in the left rear corner

[tommymonza]

These numbers were with the SS lower ? Do you by chance have numbers with a stock lower ?


Thanks for the info.

[BUIZILLA]

with two people up front the SS speeds are virtually identical with the stock drive.. :propeller:

[MOP]

Minxguy said he saw little if any difference in speed when he pulled the SS off and slapped the Alpha back his Minx his top was 60. The stern jack may be the hot ticket, they seem to help most setups.

[MOP]

Lenny how far off center is that transducer puck, they can if to close cause lose of performance. I would glue that sucker inside the hull where it can't bother anything or get knocked off!

[CHACHI]

62 MPH, one person in the boat and real low fuel, absolutly no difference between the SS and the regular alpha. I ran a 23 cleaver.

Ken

[BigGrizzly]

OK what am I missing. This boat yse to run good with that prop. I saw it with three people in Sarasota. Let me know what I missed, or did you change engines?

[Lenny]

Grizz, the boat still runs 65+-ish with me alone. It flies GREAT.

No change whatsoever.

I have 650 pounds in here and I will duplicate it exactly this weekend with the SS and sternjack on it.

I suspect a few more over what you see above.

Grizz, with stock power and 2 people, and 2/3 of a tank, and "stuff" in the FLAT calm, I don't see a problem. You never saw the TXP run WOT at Sarasota. It is too much for this boats motor currently and the stern lift is terrible. The Cleaver ROCKS.

One person in this boat and a quarter tank, no tools, is a BLAST :yes:

You're not missing anything. :)

[BigGrizzly]

So what you are saying is that this prop is too big for the application, with the added weight. So if I take all the tools, spares, complete water pump, belts, hoses,props anchors, ropes, wiring, oils, etc. , the Criterion and Corsican might actually be fast? The price is too high for me. In most cases my boat brakes at the farthest point away from the dock. Now I do understand your situation. It seems to me you need an arsenal of props. If the boat is in fact lifting the boat too high and the motor is lugging, which your 4100/53 mph suggests, The boat is actually rocking forward on the rocker. you need a smaller pitch. At this point a 21 TXP has not been made. The TXP is not a stern lifter, so I say that your boat is out of balance as BUIZ suggests with his comments. This is critical in a rocker hull. Or get more available power to the water ie smaller prop. I am just trying to explain to people propping their boats. You prop for your application and loads. In my boats I always carry a different prop for a different application, Sometimes two. There is NO magic prop for all applications. I even have a sand bar jumping prop-ask Road Trip:bonk:

[tommymonza]

Why do you guys think you are not seeing any speed increase with the SS over the stock? Is this because you lost your bow lift with it and therefore increased your wetted surface ? Are you turning more rpms with the SS?How much shorter is the SS, i heard 3 inches

[Lenny]

2 and 3/4" shorter. I would have to agree somewhat with Grizz. The boat is too wet in my test situation.

But, as Jim suggests, if there are two people in the boat, you have one sit in the back seat and that is worth 5-6 mph :eek: That should tell you something about the balance with the SS.

I am thinking the Stern Jack will allow for me to increase my hull angle and get things out of the water a bit.

This afternoon actually :)

[blackhawk]

2 and 3/4" shorter. I would have to agree somewhat with Grizz. The boat is too wet in my test situation.
But, as Jim suggests, if there are two people in the boat, you have one sit in the back seat and that is worth 5-6 mph :eek: That should tell you something about the balance with the SS.
I am thinking the Stern Jack will allow for me to increase my hull angle and get things out of the water a bit.
This afternoon actually :)

That is interesting that one person can make such a huge difference!

A sternjack is much different from an extension box as it actually brings the prop to the surface with LESS trim, having the same affect as a shorty. So, your boat may actually run even flatter an wetter with the sternjack(most boats do).

But, that is just the theory behind it and we all know that theory doesn't always work in the real world! :D

[Lenny]

A sternjack is much different from an extension box as it actually brings the prop to the surface with LESS trim, having the same affect as a shorty.

Yes, but as an 8" extension on a 12 degree transom (negative) it is actually FURTHER (deeper) into the water at neutral trim. And the Donzi is now 18' 10 3/4" long. As well, the fulcrum is moved further aft.


The Stern Jack is basically an eight-inch extension block that fits between the gimbal housing and the upper gearcase of the MerCruiser Alpha One sterndrive. This extension kit allows the prop to swing farther under the boat when the drive is trimmed down, which improves the hole shot. It also permits the prop to be raised higher when trimmed up for increased top speed. The Stern Jack increases vertical travel of the drive unit by more than two inches. Furthermore, moving the drive unit farther from the transom allows the prop to run in less disturbed water for a better bite. The setback also gives, the drive more leverage against the hull for improved power trim performance.


http://www.land-and-sea.com/articles/marine/poker-runs/poker-runs_article.htm

http://www.land-and-sea.com/articles/marine/trailer-boats/trailer-boat_stern-jack_article.htm


11-18-2001, 04:00 PM #13
Stroker


Posts: n/a

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I had a SternJack in conjunction with an Alpha SS on my last boat (18' Python Vyper which is similar to the 18 Donzi Classic) and the SternJack made a very big improvement in handling and added a few miles an hour top end. The SternJack all but eliminated chine walking at top speed (just under 80 w/built 383 cu.in. smallblock). I could drive with two fingers, whereas before, it was all hands on deck to keep the boat stable. The other variable is the prop. I found best top speed with a Mercury Lab Finished 25" Laser II, but it porpoised at midrange. I tried Mirages and Hydromotives, but the surprising winner was a Turbo Vector 25". Its blade shape and diameter is similar to a Mirage, but the handling was amazing. With this prop I only adjusted the trim tabs when I wanted a full speed run, otherwise I didn't touch them, and trim angle was likewise totally forgiving. Never a problem with blowout or turning either. My boat was much smaller than yours, but thought my experience would be interesting. One last thing, driving in rough water with the SternJack is also much safer. The prop hardly breaks free and the landings were better. The boat acted like it was at least a foot longer. Granted, the Alpha SS drive is approximately 2 1/2" shorter so the drive is naturally very high.




:confused: :confused: :confused:

...but not for long...

Here goes... :D

[Lenny]

Should look like this when I am done and find out if it actually works.

[blackhawk]

Yes, but as an 8" extension on a 12 degree transom (negative) it is actually FURTHER (deeper) into the water at neutral trim. And the Donzi is now 18' 10 3/4" long. As well, the fulcrum is moved further aft.
http://www.land-and-sea.com/articles/marine/poker-runs/poker-runs_article.htm
http://www.land-and-sea.com/articles/marine/trailer-boats/trailer-boat_stern-jack_article.htm
A standard extension box moves the ENTIRE assy back. Trim leverage stays the same and the propshaft will be slightly deeper and require more trim at WFO. A stern-jack makes the drive "longer" by mounting between the gimbal and the drive. So, at negative trim the propshaft will actually be deeper, at neutral trim about the same and at positive trim the propshaft will actually be higher. That is the whole concept behind the stern jack and it makes it totally different than an extension box. Less trim=more forward thrust and the drive being higher=less gearcase drag. Same benefits as a shorty BUT a deeper propshaft at negative trim. I think they even marketed it as a "variable x dimension" back in the day.

I think the stern jack is a very unique and interesting piece that works well on the right boats. I would love to try one. The only negative I see is far greater stress on the gimbal assy. Hydraulic steering is a must IMO. I think this is one of the big reasons they didn't catch on and sell.

EDIT: I didn't see your second quote in that post. You get the idea! :D Good luck and I hope you see some gains!

[blackhawk]

Should look like this when I am done and find out if it actually works.

That's Scott's Sunsation Dominator. He really likes what the stern jacks did for the speed and handling of his boat.

[tommymonza]

Is there visible rocker over a 6 foot area if you lay a straight edge on the bottom of a 18.Is there any hook on the 18 or is that only in the 16s outer chine

[Lenny]

Lets put it this way. If I had a lot more money, I would put on an IMCO Stern Advantage, 8" setback, twin rams, and an Imco 3" shortie on an 18 in a SECOND... :eek: :eek: :eek:
This Land and Sea Stern Jack is far better than anything I could have imagined.
Here are the stats. These were Identical conditions, flat water, no chop at all, (heavy wetted once again) no wind to speak of and all passes are an average of 2 directions. I tried both props once again. Interesting enough, the revs did NOT go up on the 3 Blade 23" Merc cleaver ( well maybe 50 rpms, but the speed did about 2.5 miles an hour !!! . The Cleaver is a hands down winner on this boat. It far outperforms the TXP. Keep in mind tho, from a percentage gain, the TXP went from 53.4 GPS to 64.1 :eek: 9.5 miles an hour faster and 500 RPMS. :eek: .They both worked much better, but the TXP, though very improved from before and a large increase in rpms was "SQUIRRLEY" when you got off the throttle. If you came off the juice with the trim up still you had a bad situation on your hands. It required trimming in as you slowed down to keep it all together. The Cleaver could give a $ h i t. It did whatever you wanted. The TXP's handling in a mid range turn was phenomonal. It was just like running on tracks. It felt that solid and I mean it would TURN and hard. No blowout and incredibly tight radiuses. The Cleaver would not and required trimming in for this kind of thing. Bow rise was FAAAARRR better with both. I could stay hooked up and trim out enough to probably create 4-6" of additonal lift. It was GREAT.
The only odd thing, was at 0 trim, and the 8" extension I assume there was a lot of baggage underwater creating a fuss. It looks like you are running two Arnesons when at 0 trim as there is soo much water flying up behind you, (not onto the boat mind you). The trim rams or drive or something makes a huge staement. The SECOND you apply trim it is all gone. The "pick-up/giddy-up" feeling is unreal. From a 3000-5000 throttle hammer, and then add trim, it does actually pin you and start to fly. :D The acceleration is soo much different than before. Hydraulic steering would be a must for me if I was going to get serious here as the drive is further back and accentuates any play or wag. The Cleaver, at WOT, has a minute amount of chine walk, but very minute. I can not imagine how well this combo would run if I had had some 2 footers or something to air it out. It was flat calm (again) and a very wet hull. Weights in the boat were identical, so was fuel. Having the passenger sit in the back port side made little difference. 760 pounds of baggage once again in the boat. 400 hours on the stock 350. Alphs SS on a SternJack.
Here are the stats for comparison to above (prior the Sternjack)
Labbed three blade Cleaver 23"
2000 RPMS-13.9 GPS-52% slip (same speed, same slip)
2500 RPMS-25 GPS-31% slip (slower by 1.1 MPH and 5% more slip)
3000 RPMS-35 GPS-20% slip (4.9 mph FASTER and 11% less slip)
3500 RPMS-37 GPS-27% slip (3.1 slower and 6% more slip)
4000 RPMS-44.2 GPS-24% slip (unchanged)
4500 RPMS-59.1 GPS-10% slip (5 mph FASTER and 6% less slip :eek: )
5000 RPMS-62.3 GPS-14% slip (2.5 mph FASTER and 3% less slip)
WOT with this prop, but with One person, 68.4 GPS in flat calm water and 2/3 a tank of gas and tools etc.
23" Turbo TXP
2000 RPMS-19.5 GPS- 33% slip (.5 mph slower and 2% more slip)
2500 RPMS-29.2 GPS- 20% slip (.1 mph FASTER and same slip)
3000 RPMS-38.7 GPS- 11% slip (.7 mph FASTER and 2% less slip)
3500 RPMS-45.7 GPS- 10% slip (2.3 mph SLOWER and 4% more slip)
4000 RPMS-54.5 GPS- 6% slip (1.1 mph FASTER and 2% less slip)
4500 RPMS-61.2 GPS- 6% slip (whole new territory for this TXP prop)
4650 RPMS-64.1 GPS- 5% slip (whole new territory for this prop)

That was WOT. I gained 500 rpms with this extension box and the TXP and 10.5 miles per hour Too bad the prop is still to hard for the engine to turn it and it is scary coming off of WOT while trimmed out.)
As I said, this boat likes the setback. Anyone got $10K to lend me for the IMCO? :D
Now the motor comes apart, tomorrow, and I am having a pile of stuff done.

I would still like more Stern Lift. Would a 4 blade Cleaver give more bow lift? What prop (or mod) will? Very happy with this thing. Does cup or rake give you the bow lift?

What I have learned here is this; The Cleaver plays nice, but didn't see a huge gain. The TXP is scary slowing down and a bit messy to watch from a water propulsion standpoint (spray) but saw huge gains. It is trying to tell me something but I am too stupid to figure it out. Something about that prop loves this 8" length and the new surrounding water. The motor picked up 500 RPMS :eek: and 6% slip numbers :eek: So, what is it that made it so happy, and what else would work similarily but not create a white knuckle experience coming off speed with the trim out?
Grizz?

P.S. the Cleaver, yet with smaller gains, felt perfect on the hull. (Short of turns while trimmed out.)

[smokediver]

Great info and post ! I wonder if running a hydromotive like Rootsy ran on his 16 would be any different ? kind of a cleaver blade or maybe a Rev4 ?

[BUIZILLA]

so your saying a Bravo Scorpion boat with the IMCO setup you described is the ticket? :)

[Lenny]

so your saying a Bravo Scorpion boat with the IMCO setup you described is the ticket? :)

...YES... ten times over

...or find a Stellings Stand-off box and a Bravo... http://www.stellingsmarineproducts.com/

...or a deal on this... http://www.imcomarine.com/pages/extensionboxes.html

...or one of these from Latham http://www.lathammarine.com/extension-boxes/KEXB-7979.jpg

[BigGrizzly]

Lenny, a smaller TXP may be the ticket, but one has not been made. Maybe a Lightning. That boat didn't like it with out the stand off maybe that would change. As for the situation of slowing down, that is because of the less slip causing the steering to be over taxed. Since the clever has so much slip it affects it much less. case in point, the TXP has much more power in reverse then the clever. I am not too surprised with the gains because you are now able to get the rocker out of the water and on the stern and make the hull work. Normally at higher speeds the 18 flair on the bow helps to lift the boat to air it out even on calm water. From what you describe and knowing you I would say that external hydraulic would be a must. The steering would add speed to because of fishtailing. The slow down heart stopping pull would decrease or stop. The slip differences are major. As for which prop I would use, Do to the handling at mid range and lack of slip I would go with the TXP. Remember you don't always have to go fast but you always have to turn, especially in an avoidance situation. Just a note your boat has had the most improvement of any that have been really documented correctly and in that size range. I have heard of big numbers before but when I have tried to verify it they always come up way short of the stated mph.
Now stern jack Vs setback. The angle of attack of the lower unit to the water will be different due to the pivot angle to the hull. At this point it is hard to say which would be better, there are arguments on both sides and equally strong. The IMCO system is a really nice piece, Garry has installed many of them. Nice but expensive.

[BUIZILLA]

I think there is a Fusion around here someplace....

[BigGrizzly]

Yes you do.:wink: That is a viable option for this rig

[MOP]

Lenny am I off on the math?? The boat did 65 prior to any mods, now it does 68.4. 10 with one prop but 3.4 overall, I am willing to bet there is another couple left just need yo play more.

[Lenny]

Mop, the 68.4 is one person. Not the two people the rest was all done with. I thnk the 68.4 would be 70 if I had had another 1/4-1/2 mile to play with. As it was, I was shore to shore and embankments were the next order of the day :eek:

All the ducks were not much fun either. We went into one group of them, at about 65, the all flew up a bit then turned into us. :eek: We both "ducked" :D and went right through them. There "were" about 20 of 'em. Probably just over half that now. :(

I did not want to do the "FABIO" and take one in the face at that speed.

So, to answer your question, yes, with some more room, and NOT a glass calm day, salt water, not this junk, :D 1/4 or less tank, remove the 50 LB tool box from the bow area and pull up the port tab, (YES, I was always dragging the port tab for balance, and in all speed runs without changes) I bet I could see 72 with this Cleaver and the SS.

Not too shabby for a 20 year old boat and motor with 400 hours on it.

I really want a stand-off box on this thing. 8" and hang a Bravo out there with a 3" shortie from IMCO. Wanna give me some money ??? :D

[DONZI]

I am glad you gave the Sternjack a try. I was wondering if it was going to remain un-used when i spoke with ya at the Dust Off.

A couple more benefits you will see with that combo is the great fuel mileage with those low slip #'s. Also when you have a full crew onboard and still have the ability of slow cruise w/out falling off plane.

Kinda odd to see the similiar Cleaver #'s at the 3500 rpm @ 37 mph .This is pretty much where i am now with my current set up and the slip #'s going down as speed increases. It's also a lil ironic i lost about 10.5 mph removing that combo and you gained it. Nothing a lil H.P. increase can't cure.L.O.L.

I had good luck with the Turbo 2+2 and SS W/Jack but my 22 probably needs more bow lift than the 18. But my be well worth a try.The Lightning look's like a larger blade area that i have found can cause that excessive prop torque.Causing the slow down symptons.
The 4 blades are a lil tougher on the Alpha on re-entry also but was the best all round performer for me.

I think you'll have a smile on your face after you get it out in the rough also.








Ken







..

[chappy]

Great thread all around. I've learned a ton.

[MOP]

I am picking up on Scott saying the extension boxes just moved the drive back but left the prop shaft height the same. I "thought" I had read the they were adjustable to raise the prop shaft. ????

Phil

[Lenny]

MOP, they have standard (no raise) and 3" raise. So, you could put on a 3" raise (8" long) extension box and a stock Bravo lower and be where I am now with the Alpha and SS. But, you wont have the low water hydrodynamics the SS has. And, your pivot in my setup is similar to an Arneson in length from stern to prop, whereas the extension box drive will pivot from where mounted at the end of the casting.
I do know that Lipshultz's Cig, with all this stuff and a 540, RAN. They all had IMCO extension boxes and Blackhawk drives.
The Sternjack seems more along the lines of this in design. http://upload.wikimedia.org/wikipedia/en/thumb/b/b7/Longtailboat.jpg/800px-Longtailboat.jpg

[BigGrizzly]

Lenny what has me a little concerned is the slip of the clever is higher at WFO then one notch down, it should be the other way around lke the txp. If you like the 2+2 I have some really good prices on some sizes of them-over stock situation

[Lenny]

Grizz, I am all ears,... and remember, I want BOW LIFT in whatever you have in mind. I would also like to be able to get to 5000 with it.

[BigGrizzly]

Several options. IF you use the stern jack the props will differ then with out it , but you know that. As we have discussed testing is where it is at. Now with out the jack your boat didn't like the lightning with one person in it and no stern jack. It is a bow lifter, the other is Maybe a 2+2 would work, it is not normally used on that application but with a jack either may work well. Maybe even a M+ might do it. Now the Fusion will plant the stern and be at high speed like the TXP is at mid range. I don't remember what I sent BUIZ, A 23 might be too big in the Fusion a 22 in it or the 2+2 is abetter optopn since the TXP is still lower RPMs.

[BUIZILLA]

this Fusion is 14.5 x 23

a stock mouse won't push that thing...

[blackhawk]

I am picking up on Scott saying the extension boxes just moved the drive back but left the prop shaft height the same. I "thought" I had read the they were adjustable to raise the prop shaft. ????
Phil

Phil, I haven't kept up on extension boxes lately. IMCO offered both the standard and 3" versions but with the 3" you had to raise your motor. Stellings had an "adjustable" box and maybe others do as well now.

Like I said in my previous post the big difference between a extension box and stern jack is WHERE the extension takes place. The stern jack mounts between the gimbal and the drive so the prop is closer to the surface with the same trim angle.