help reducing slip

[wrestler20]

Just wondering if anyone has any ideas on reducing slip %. I have a 20 foot 91 astro fsx fish and ski. I am running a 1992 Johnson 200hp gt motor with a 24 pitch raker. I have a 10 inch hydraulic jackplate and am turning 5500 rpm wot. The problem is that the boat is only going 51 mph. When checking the slip calculator, that puts the slip at around 25%. Seems like to get that percent slip, i would have to forget to pull the anchor up! I have tried checking the bottom for any irregularities and it seems fine. I have tried waxing the pad, to no avail, so then tried sanding the pad with 1000 grit sandpaper to no avail. Anyone with any ideas on how to get this pig moving any faster? Kind of embarrassing to get passed by 17 footers with 115hp on them all the time.

 

[ob]

Re: help reducing slip

Overall , rig weight and design is a criteria in selection of prop pitch and style.Raker props are primarily used on boats that fit the category of high performance.(ie,low weight to hp ratio)<br /> I would recommend changing to a conventional OMC sst2 prop which is double cupped.One of around 21" pitch is probably a good starting point,although only a water test will confirm the final selection.<br /> My friend runs a 200 johnson on a 21ft flats rig with a lightweight console enclosure and uses an OMC sst2 19" prop that pushes his rig right at 50mph at WOT.

 

[wrestler20]

Re: help reducing slip

Hello, i started with a 21 pitch omc stainless prop and could over rev too easily. I trid a 23 and could still go just above where i feel comfortable on rpm's. I then tried a 26 Raker and could only turn it to about 5100 rpm. the 21 topped out at 45mph and the 23 ran it to 48mph. the 26 at 5100 was about 49mph and the 24 seems to be the fastest so far. i did try a 4 bladed 21pitch also that ran at about 45, but it wanted to run so high in the water that i began loosing water pressure, so i didn't want to run it any higher tosee what it would top out at for rpms and mph. The four blade was sluggish coming out of the hole though, i know that it shouldn't be that way and should have better acceleration, but that wasn't the case with the one i was using. Thanks for the reply though.<br /><br />Steve

 

[chuckybaby]

Re: help reducing slip

Wrestler, did you do anything with your transom ?<br />Post some pix if you have any. I have the same trb with my 89 Procract 1950 fishnski. Am running<br />25 pitch raker with about 25-30% slip. It's truly<br />pathetic !<br /><br />I think we need lots of cupping to get the lift required to get these pigs out of the water. I'll be trying 20 to 24 pitch 4 blades when the water is a little softer up here

 

[Waterbugtoo]

Re: help reducing slip

wrestler20,<br /><br />If you are relying on the boat speedo telling its 51, you are pretty much barking up a tree. Using a gun, I have yet to see a speedo in any boat that was dead on accurate, even the paddle wheel type. Speedos can be as far as 10 or 12 MPH off up or down, even more if junk is in the hose or inlet. Also, Astro's are not exactly the sleekest in high speed hull design, but many factors can affect speed. Weight, trim, motor height, prop, etc. If the prop is actually dealing with that much true slippage, the main cause of that is obviously air. A nose cone or low water pickup can help tremendously in that instance. Your prop hub could possibly be slipping as well, but usually that will not continue operation very long at all. You would know if that was the case. As far as prop selection, you cannot have the best of both worlds. 3 blade for top end, 4 blade for low end. Only an expensive shift prop would favor both ends, but they still have their limits. Is the Astro designed for such a jack plate? Call them and see what they tell you. These are just a few things to look at in determining the answer to your question.<br /><br />

 

[wrestler20]

Re: help reducing slip

hey chuckybaby!, guess you havn't found the solution yet either. I did end up getting the money from the insurance company to fix the transom. It ended up being $4700 to fix it. The said the stringers were good and that there were no structural problems with the hull as far as any warping from the bunks. The only thing they did say was that the astro and the procraft hull were just never that fast. They also said that most fish and ski's of that length and hp would probably only be around the 60 to 65mph range at best. I don't know if he is right or not, but he seemed pretty informed about it.<br /><br />Waterbugtoo- I am using a gps for the speed readings. I have thought about the nose cone with the low water pickup so i can raise the jackplate a bit and keep water pressure. I am just afraid of the amound of running i do on the mississippi river and the fear of running it on sand with the low water pickup. As far as if it was designed for the jackplate or not, i have no idea. It did pickup speed and improve holeshot when the plate was installed, before i hit a log and am in the middle of rebuilding the transom. All of the props that i have tried have been new, so i don't think any of them had any hub problems. As far as contacting astro, they have to be the worst company in the world to get info from. They actually told me the last time i called with a question that they do not have any of the records from when they were making "those" boats. I assumed they meant bass/fish and ski boats. They couldn't tell me anything about my boat. Sorry this doesn't sound like much help. Thanks for the help though, any ideas are worth trying.<br /><br />Steve