Speed?

[jjasonlfine99]

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I just bought a 92' Astro 18DCX with a Merc. 150 xr6. Wondering if anybody knows what would be the best prop to put on it to get the most speed without completely loosing hole shot. Thanks!

 

[studlymandingo]

Re: Speed?

In order to give you any kind of answer you will need to answer a couple of questions so everyone has a starting point.

What is the current WOT RPMs of your boat?

What is the current speed of the boat at WOT?

What is the current prop type and pitch? (Alum or SS, brand, etc)

What do you use the boat for the most?​

 

[jjasonlfine99]

Re: Speed?

I just bought the boat so i can't tell you speed. It came with a 24 pitch ss prop but it has a bend on one petal. The boat will be used for fishing no tubing of any sort. I would like more top end than hole shot but a reasonable compromise between the two.

 

[Esox]

Re: Speed?

Have the current prop repaired and then test with that prop and get the info you need to answer the questions Studly asked. Then maximize the setup with the current prop. Then look into testing different props.​

 

[jjasonlfine99]

Re: Speed?

Thanks!

 

[Silvertip]

Re: Speed?

He was told to post speed and MPH info over on the outboard forum and ignored the request. Geez -- Jason, pay attention. What do think we are, mind readers! For all you know you already have the best prop. If the tach says the engine is reving at the maximum recommended WOT RPM you got what you got. More pitch lugs the engine. Less pitch over revs it.

 

[jjasonlfine99]

Re: Speed?

Sorry, i have not even picked up the boat yet and the prop thats on it is messed up. Was looking to pick a new one up today and was after advise on a good starting point. Im not a expert thats why im asking questions here. Won't bug you guys anymore.

 

[Silvertip]

Re: Speed?

You aren't bugging us -- just not being up front with us. Your question would have been appropriate had the engine not had a prop at all. Then you have no starting point of reference and you could rely on someone to at least get you in the ball park. However, the prop that's on the boat now is your starting point. It has numbers on them. Go from there. You should have mentioned in your first post that you didn't even own the boat yet. Then when told what to do you went ahead and posted the same identical question on this forum anyway. In the future, when you ask for help, make sure you tell the full story. We can't see your boat and most of us don't like having to "pull" information by the spoonful from posters. That takes time and is very frustrating -- at least to me. We do need some data to work with. Buying a prop is like buying shoes. One brand of 9-1/2 may not be as good as another brand of 9-1/2 on your feet.

 

[Esox]

Re: Speed?

Well said Silvertip ​

 

[Silvertip]

Re: Speed?

I certainly don't mean to ruffle feathers, but cruising through this forum you will find it mentioned time and time again that for us to provide reasonable prop recommendations they need to provide the type of boat, type of engine, current prop style, diameter and pitch and at the very least, what the current wide open throttle rpm is and what the top speed is at that rpm with an average load. One post later someone asks whats the best prop for a xxxHP Johnson and provides no other data. The year of the engine is important because it determines the engine gear ratio which is required in a prop calculator. Drives ya nuts when folks don't follow directions or they tell you half the story and then expect a logical answer and get uppity when they don't like what they hear. I frequently suggest that boaters buy a service manual specific to their engine if they intend to work on it themselves. About 1 out 10 respond like I just asked them to rip off an arm. It must be Friday and therefore time for a beer. That's right, I already had two.

Hey everyone -- have a safe weekend on the water and if your weekend is the start of a July 4 holiday week, be doubly careful of the IOTW (Idiots On The Water).

 

[Esox]

Re: Speed?

I agree 100% with you Silvertip. I don't think your ruffeling any feathers - just calling it the way it is. You spend a lot of time on this site helping people out and your frustration is understandable. There is a post in the Engine FAQ forum titled "Prop Selection, By Walleyhed" with some great info in it. It sould also be pinned at the top in this forum. There are, however, a few on this site that can recommend a prop without the poster giving any info at all. How they can do that is beyond me. The people that know what they are doing need to have the data before they can make suggestions. OK. Time for another beer . Have a good weekend!​

 

[jjasonlfine99]

Re: Speed?

i understand that dealing with the uneducated like myself must be frustrating. I really have no one else to ask thats why i went searching and found this web site. I am new to the slang that is spoke here im trying to pic it up.

All right i got the boat from the dealer today(92'Astro w/ 92' 150hp xr6) took it to the lake and it ran 55 WOT @4900rpm. It has a 24Pitch Laser prop and a whale tail thing on it. After reading as many threads as i could find on this subject i came to the conclusion that it is over proped and i need to go to a 22Pitch. Because its a xr6 and has the smaller lower unit which has the smaller barrel prop I could not find a prop locally. So monday im going to have Midwest Prop. change the pitch of my laser to 22. I took off the fin hoping that might increase the rpm's also. I don't know the dia. of the prop i looked on the outside and don't see it. Am i headed down the right path?

http://s127.photobucket.com/albums/p135/jjasonlfine/?action=view&current=img025.jpg
This pic does not show very well that it is mounted about two inches above the bottom.

 

[Silvertip]

Re: Speed?

Before spending money on a prop, check engine mounting height. If the AV plate is flush or below the bottom of the hull, the engine needs to be raised. That will gain some rpm. when you start raising the engine though, you need to pay attention to water pressure. If you don't have a gauge, add one. They are cheap and also give you an idea of general water pump impeller condition. Making sure the engine is in a good state of tune may also pick up some revs.

 

[180shabah]

Re: Speed?

Is that 4900RPM with a damaged prop or has it been fixed?

That can make a huge difference.

 

[Ron G]

Re: Speed?

Before spending money on a prop, check engine mounting height. If the AV plate is flush or below the bottom of the hull, the engine needs to be raised. That will gain some rpm. when you start raising the engine though, you need to pay attention to water pressure. If you don't have a gauge, add one. They are cheap and also give you an idea of general water pump impeller condition. Making sure the engine is in a good state of tune may also pick up some revs.

Very good info silver!once all this is done and the numbers are there.you need to look into a jackplate for sure.an 18 ft with a 150 you need a jackplate!and it will make it easyer raising and lowering the motor to fine tune her in!!congrats on the new boat now get to testing and we'll be here for ya!!!

 

[jjasonlfine99]

Re: Speed?

Thanks a bunch guys i'll start looking for a jackplate.

 

[jjasonlfine99]

Re: Speed?

Will 6" of set back be sufficient?

 

[Silvertip]

Re: Speed?

I think you misunderstood what engine mounting height (or the "X" dimension) is. You have the engine tilted up. You need to have the engine tilted down. Place a straight edge along the bottom of the hull (along the keel) and pull it toward the engine. The anti-ventilation plate on the engine should be as a minimum, flush with the keel to a couple of inches above it. The AV plate is the flat plate just above the prop.

 

[jjasonlfine99]

Re: Speed?

O..lol ya i was way off. I'll check here in a bit. Thanks!

 

[jjasonlfine99]

Re: Speed?

alright the av plate is aprox. 2in. above keel. I took my 24pitch laser to my prop man and had him knock it down to a 22pitch. when i picked it up he informed me that two of the three petals were of 3\4'' off. while he was doing that i had a water pressure gauge installed and a new water pump. I took it out and it ran 60 wot at 5100 rpms. I liked the 5mph increase but surprised that going from a 24pitch to a 22pitch only got me 2k rpms. I also found that my thermostats are going out, after running up the lake the pee hole was sputtering and the water was pretty hot. Im going to attempt to find some tommorow and install.