18 classic, Alpha, and stern jack

[harbormaster]

I have been looking stern jack for my 18 classic's Alpha outdrive. Anyone have any experience with them? What are the pros and cons?

[Greg K]

Funny, I just posted this link in the Alpha SS topic about a stern jack.. Land & Sea (http://www.land-and-sea.com/marine/stern-jack/sternjack.htm)

[Ranman]

Scot, I looked into these a while ago. Did you search for previous posts? :D They are expensive and it is my understanding that on an 18 Donzi your handling will be improved, but top end gains are small 1-2mph. If PaulO is around, I think he may know more about them.

[TRU-JACK]

Just finished reading the link Greg provided, and thought they might be good on a 16, as i can't find an alpha ss. I'm interested in their performance on a 16 if anyone knows. thanks

[PaulO]

I'm here!
Ranman is correct. I spoke with quite a few people with different boats similar to Donzi 18s and one actual Donzi 18 owner who installed the stern jack. No one could honestly confirm any speed increases although all said that handling was improved. A lot of money for something that can't be quantified (in my opinion) and that would seem to put considerable extra stress on the gimbal assembly and steering components. Looks like Scot has really gotten the "speed" bug!!!!
PaulO

[CDMA]

I have experience with one on an 18/Alpha. I did back to back tests and it has been on my list of stuff to type up...it just went to the top...give me till tonight.

Chris

Sleep deprived.... to the ninth degree divided by the inverse tan of the secant....nevermind...

[harbormaster]

From what I can tell it seems to be a quick way to improve handling and gain about 5mph

[Rootsy]

all ears... errr i mean eyes... wink

[McGary911]

An 18 with a stern jack\alpha was just posted in the for sale section. Hopefully, he'll check the perf talk forum as well. Check it out, you can see the jack in one of the pics.

[Ranman]

Scot, The stern jack is expensive $2000 (alpha) $2500 (Bravo), plus you have to modify your trim rams or buy new ones. I think they work better on some boats than others. Reports seem to indicate an improvment in handling on an 18 Classic. I don't know where you get the 5mph increase from as that is counter to anything I've heard regarding Donzis (maybe on another hull??). I would not expect that type of increase on an 18 Classic. There's also a question of the Stern Jack's impacts to the Gimbal and steering components. It acts as a lever and potentially places a lot more stress on the above components. The bottom line is, the stern jack will provide some benefit to our boats. However it may come at a big cost. If it is a big speed gain you are looking for, your $2000 may better be spent elsewhere. Keep us posted on what you come up with.

[PaulO]

Buy a used procharger with the $2000 instead and gain 10+ mph!!
PaulO

[harbormaster]

I looked at adding a procharger, but then you risk blowing your Alpha outdrive, and then need to go with a bravo.

At this point, It seems the sternjack does not decrease the life of the outdrive or engine.

You naysayers have a better idea to gain better handling and 5mph for 2500.00?

seems to be a more cost effective price that adding a procharger, bravo, and shortie.(at least 10 grand!) Hell I might as well sell the boat and use that 10k to put towards buying a 22.

Woodsie, Have any good ideas or constructive suggestions? Didn't you put a blackhawk on your boat??

[CDMA]

Here it goes:
This summer I met this really odd duck out by me with a 1986 18 classic alpha. The boat was powered by a 260 merc with 400 hours. The fellow had just bought the boat and had grand plans. The first thing he wanted to do, and there was no talking him out of it, was to install a stern jack. Now this guy was not mechanically inclined so I smelled an opportunity. I offered to install the Stern Jack for free under the condition I could do before and after tests of the boat. He gave me the keys and $2200 and said “ call me when it is done”. Oh goody….

I ordered the stern jack and while I was waiting for it to come I figured it was test time. I took the boat out and while I did not want to beat on someone else’s boat I put the boat through a full test. Got a max of 59.3 mph @4900. The boat ran well but the engine felt a little tired ( well maybe I am just so used to the 383 now wink ) . The handled the same as any of the other 18’s I had driven and I noticed no real significant differences. At WOT full trim she did not have a tendency to chine walk but if you got in a cross wake you could feel it start and needed to steer out of it. Boat more or less felt and drove how I expected.

It took 2 weeks for the stern jack to come but once it came installation was a snap. Not really difficult at all. The most difficult part was taking the rams to the metal shop and trying to get them to weld them this year.

Once the installation was done I called the owner and asked if he wanted to try it out with me. Said “thanks but no thanks….let me know how it goes” Ok so off to the ramp we go.

It was a Friday evening and there was a fair amount of boat traffic out but otherwise conditions were similar to the previous test. I noticed no perceivable difference at slow speeds but granted we don’t drive our Donzi’s slow long do we…

Out the channel I went and onto plane. No difference yet. Seemed to plane off about the same and react to trim more or less the same up to about 30 mph. Above 30 I started to notice some differences. However first let me state that with the stern jack installed and the same prop the boat ran a blistering….60.9. I tried and I tried but there just was no real speed gain to be had. I tried different trim angles, tab settings you name it.

However being a beautiful night and someone else paying the bill I figured might as well get some seat time. Despite the disappointing speed gain by the end of the night I was sold. It took the standard handling 18 and moved it so far above and beyond what I have come to expect I was speechless. My real vice with the 18 is that where I boat I deal with lots of cross wakes, confused seas, and basic garbage. While I find my 18 does well in a chop I find that at high rates of speed confused seas really can get to her ( right Diana??). I was truly impressed with the difference. The longer I drove it the more comfortable I was keeping the hammer down over waves I previously would have seriously slowed down for. Also of interest now I could not even if I tried get the boat to chine walk. I could over trim her, hit wakes, do basically anything and nothing would even create the slightest hint of chine walk. Stability was increased, turning was improved and generally all around handling was far superior.

But I still had to deal with the owner that just spent $2000+ for a boat that didn’t go any faster. I called the guy up and explained to him what I found. He sounded disappointed but was very nice and said it was worth a try. He later called me and said basically the same thing I did…no faster but sure a lot easier to drive.

So now that I spent $2000 of someone else’s money what do I think? I have mixed feelings. There is the issue of the gimble wear and strength. I looked into it as best I could and from what I can tell the actual strength of the gimble is sufficient to add the stern jack ( this is only applying to our smaller lighter boats…not necessarily 33ZX’s). Now you can hem and haw about what the gimble was designed to do but in reality I don't care what it was designed to do I only care what it can do. I really doubt that anyone would ever break the gimble but what I do think is that there will be a significant increase in gimble and gimble ring wear. If I was using this on my boat I would probably resign myself to rebuilding the gimble every 5-7 years. Not the worst thing but still an issue.

I think that on the classics ( at least the 18) a stern jack should not be looked at as a measurable way to increase speed. If you want to go faster w/o adding power look for an SS. However it is more important to me that my boat handles well then goes fast and if you have the same feelings then maybe a stern jack is for you. There is no arguing the increase in control, stability and handling that I encountered.

So why don’t I have one on my boat? Well a few reasons. Mainly money. They are a stiff shot for sure. I think if I came across a used one for a good price I might go for it but there are things I need/want for my boat before a stern jack..

Your resident Naval Architect in training... wink

[MR MAGOO]

A buddy of mine has a 24 Donzi Spitfire. He installed a pair of 1987 320EFI motors with Alpha SS drives and Sternjacks. The reason he went with sternjacks is that the SS drives were a little high and with the sternjack, it would plane off much faster. He is running 23 Mirage plus props 5600 rpm. It handles beautifully and doesn`t do anything funny.

[Rodger]

A fellow I know installed a Stern Jack on a 20' Cigarette that has a low boost turbocharged 350 S.B. Alpha Drive. He couldn't say for sure whether the Stern Jack helped much to increase the speed because he made all the changes at the same time. He did though, notice a big improvement in handling and general boat attitude. In fact his 20' handled quite a bit better in cross waves and messy chop than my 22'.

[BigGrizzly]

Now do you thinit will handle better than out side steering- I think not. and the strengthen the gimbles. Illtellyou the hydraulic steering is amaizing