Took a test drive in a Ranger bass boat that a guy was selling and I'm wondering what was going on with the motor. I don't know the particulars on the prop so maybe there's no answer without them. The motor ran great on top end, but out of the hole, just about the time the bow was settling down, the rpm's would spike and lose power. If I eased back on the throttle about the time it was settling, it would be ok. Is that ventilation and if so, what causes it?

That's called cavitation. It either has a prop problem or a setup problem, UNLESS, you were not trimming it in, or trying to trim it out too fast as it's laying over.  I like to come out of the hole and start trimming out just as it's starting to lay over.  It makes the motor cavitate slightly so the rpm jumps up a little but then it's gone like bullet.  Get it right and it sound neat.  Get wrong and you blow the prop out and have to throttle back, let it catch and go again.

 Then it could be the prop.  I have a 26" raker that runs on my 225 just fine, put it on my modified motor, and it does just what you are saying, you have to nurse it on plane.  I had to install a hydrofoil to get it to come out of the hole until I had Bob Lipton tune me a prop for it.  The dorky looking hydrofoil helped the hole shot so much, I put it back on even after getting the tuned prop.

Cavitating. Prop or trim issue. 

I'm thinking about buying this rig. Is it a black and white issue? Meaning, find the right prop and problem solved, or are there other factors such as weight distribution, motor height, etc.

How do I know what the problem is? If I need a new prop, that's fine, but how will I know that's the issue. Will I be able to try different props or an I just out the money if it still doesn't fix it?

Way2slow, if I get you the information on the prop, will you be able to tell me if it's not the proper one, or do I start with a hydrofoil and go from there?

Jeff. What motor are you running? What size prop.? Lower your motor to a level position then take a yard stick from the botton of boat to the ventilation plate on motor and tell us if it's level or if it's higher and by how many inches. This can answer some of your questions.

Does the boat have a jack plate?

I wouldn't buy a hydro-foil or a prop until you figure out the issue.

9 minutes ago, GaryH said:

Jeff. What motor are you running? What size prop.? Lower your motor to a level position then take a yard stick from the botton of boat to the ventilation plate on motor and tell us if it's level or if it's higher and by how many inches. This can answer some of your questions.

Does the boat have a jack plate?

I wouldn't buy a hydro-foil or a prop until you figure out the issue.

This may help

 

If the prop is black it's aluminum. The seller may have put on a stock aluminum prop and kept SST prop, ask him. Does the boat come out of the hole OK when the owner drives it?

Tom

I will get more info when I get home and post it. Thanks guys.

That looks like a plain Jane general purpose aluminum prop.  Even if was working, that prop needs to go in the back as a spare.  Do a little research and see what prop most are getting the best performance out of on the same boat/motor combination.  That one fits in the grocery getter category, it gets you there and back but don't expect more.

As WRB stated, looks like someone is pulling a prop swap and wanting to give you a $200 prop in the place of a $600 one.

With that being said, if the boat was setup for a high rake, cupped, SS prop and they just slapped that one on, the motor is most like set too high.  To run that prop, the motor will probably have to be set so the prop shaft is at least 4" below the pad and maybe lower. 

With the right SS prop, you will be amazed at the difference in performance .  Hole shot will be better, it will pop the bow and hold it when you really want to air it out and will probably see several MPH more in speed.

Now, don't just run down and buy any SS prop, the reason there are so many different ones, every boat and motor combination from every manufacture has different characteristics that make them do better with the right prop.  On that boat, you need to be looking at high rake props that give good bow lift, and some stern lift. 

If Bob Lipton still owns Performance Props in St. Charles, give him a call and see what he might have or can recommend for you.  The guy was a magician when it comes to making a prop work.  

One note, that sounds like a very nice boat, did you ask if it has a hydraulic jack plate.  If it does, go down on it and make sure the motor is fully tucked.

Those aren't my pictures. I will get that info up here later. Sorry for the confusion.

OK,

One thing, if you are taking pictures of the actual boat and motor.  Let me suggest a couple. 

Take one of the vent holes in the prop.  Those are the holes on the back side of the blade if it has them.  Some props have interchangeable vents and if they are all out, the holes are massive and will cause your problem.

Get down at the rear of the boat so you are level the bottom of the pad and take one of the motor from the center of the back.  Want to see about how far the prop shaft is below the pad.

Take one from the side with the motor trimmed all the way down/in so we can see about what angle it is fully tucked.

Take couple of the prop from the exhaust end, up close so nothing but the prop is in the picture.  Want to see condition and cupping on the blade.

Now, if it's a black prop like in the picture above, don't bother, it's not going to have any of the things I'm looking for.

I'll be taking all those pictures tomorrow.

Let me throw some fuel on the fire.  Have you already bought this boat, or just test driving it?  If you're test driving it, you need to have some with you that has a little more experience than you do when you're running the boat. It sounds like a relatively simple issue to solve, and if you like the boat, buy it.  But, it could be anything.  The boat could be a total POS.  You haven't told us anything about the boat, except it's a Ranger.  Not near enough information to provide you anything other than random chit - chat.

If you've already bought it, get some info out to the guys on the board, take out a loan at the bank, and get after it. 

1 hour ago, mcipinkie said:

Let me throw some fuel on the fire.  Have you already bought this boat, or just test driving it?  If you're test driving it, you need to have some with you that has a little more experience than you do when you're running the boat. It sounds like a relatively simple issue to solve, and if you like the boat, buy it.  But, it could be anything.  The boat could be a total POS.  You haven't told us anything about the boat, except it's a Ranger.  Not near enough information to provide you anything other than random chit - chat.

If you've already bought it, get some info out to the guys on the board, take out a loan at the bank, and get after it. 

Gasoline weighs 6.3 lbs per gallon, oil 6.4 lbs/gal. Add 85 more lbs of tackle.

Tom

18 hours ago, Way2slow said:

OK,

One thing, if you are taking pictures of the actual boat and motor.  Let me suggest a couple. 

Take one of the vent holes in the prop.  Those are the holes on the back side of the blade if it has them.  Some props have interchangeable vents and if they are all out, the holes are massive and will cause your problem.

Get down at the rear of the boat so you are level the bottom of the pad and take one of the motor from the center of the back.  Want to see about how far the prop shaft is below the pad.

Take one from the side with the motor trimmed all the way down/in so we can see about what angle it is fully tucked.

Take couple of the prop from the exhaust end, up close so nothing but the prop is in the picture.  Want to see condition and cupping on the blade.

Now, if it's a black prop like in the picture above, don't bother, it's not going to have any of the things I'm looking for.

Guys

I sent him that pic so he would know where and how to measure his motors position. That's just a generic pic from a website. Since he isn't familiar with boats the more accurate info he can give the more we can assist. 

If he hasn't purchased yet the best advice was already giving. Have someone who knows boats go with him to help check it out.

Ok guys, here is the info I could get.  I measured from the bottom of the hull to the ventilation plate on the motor. The motor is 3" above the hull. All 3 vent holes on the prop are open. The prop to me looks like it is in great condition. I don't see any nicks or damage at all.

Here's a shot from behind.

This is the last picture I  was able to get. Sorry they weren't all in the same post. I couldn't get them any smaller and it wouldn't let me send more. I couldn't get a picture with the motor trimmed all the way down because of the trailer. I wasn't able to get on the water again and check out the top rpm's. I'd assume that is a big factor in determining if it is the correct size and pitch. Any ideas you guys have would be great.

By the way, I did buy it!

Well, there are certainly worse props than that old Laser II and it does look in good shape. 24 pitch is in the right ball park.  Still can't do anything but chit chat without some basic information.

 

What boat is it?  How old is it?  What motor?  How old?  I assume a Mercury.  Does it have a jack plate?

 

Just guessing, absent any major damage to the boat, you've just got to get out and play with it.  I would not start spending money randomly until I had at least a basic idea of what I was trying to fix.  If it has a jack plate, you can do lots of adjusting.  If it was mine, I'd put new plugs in it.  I have found over the years that outboards like new plugs.  Then I'd get in the water and have at it.  Be careful if you haven't driven a fast boat before, but sooner or later, you'll be changing underwear.  Have Fun !!

 

Congratulations on buying the boat.  It's always exciting to have a new, at least new to you, boat to play with.

One more personal comment.  Don't get caught up in speed and performance. You can squander money in a hurry trying to go a couple miles an hour faster, and find out you really didn't need it anyway.

 

Get the boat out. Get comfortable with it, and then start tinkering.  How much crap you put in the boat and how you load it can be major issues in how it performs.

 

I had an old ZX200 Skeeter (2002).  Heavy, it was a dog.  Had the 2.6L HPDI.  Just not enough motor.  Half full of gas, lighten up the tackle store a little, and it ran like a bat. 

 

Main thing is to have fun.

-1993 Ranger 372V

-Boat is in great shape, no hull damage at all

-Mercury XR6 150hp

-No jack plate

Seems like a good set up. Prop is right size for the 150 merc and a 18' boat. As mentioned above get out on the water and make sure your trimmed down all the way until your on plane. Remove any un-needed weight in the rear of the boat. If it still cavitates trying to get on plane, I'd lower the motor approx level with hull. And see how that feels.

 

The way I measure prop height is, park the boat on a level surface, using the tongue jack, I level the boat by holding about a 4' level, 2' if you don't have a 4',  on the bottom of the pad (very bottom surface of the hull).  Set a level on the anti-cavitation plate and level it with the trim.  Then I measure from the surface up to the bottom of the pad.  Then measure from the surface up to the center of the prop/prop shaft.  Subtract the prop shaft measurement from the pad measurement and that gives you distance the prop is below the pad. 

Just what the motor should be set at is dependent on a whole slew of things, the boat itself, the set back, type prop, how much cupping the prop has are three of the main ones. 

It's been many years since I've messed with a Ranger, but they used to be real sensitive to the type prop to get good bow lift.  They had an eight inch limit on the size jack plate you could run without voiding the hull warranty, of course I think 27 years has probably voided the warranty anyway. 

First thing you need to do is make sure the motor is trimming in fully. The mid section should be at a noticeable inward angle toward the front of the boat.  If it's not, make sure they don't have the trim stop out a couple of holes.  From there, with no jack plate, I would probably try the prop and about 4 1/2" to 5" below the pad. 

It just seems strange the person you bought the boat from operated like that.  Have you asked if that was the way it did with him, because it really sounds like operator error. 

If the 3" measurement is accurate the prop CL is about 4" below the pad surface.

The prop and setup isn't too far off meaning if the trim is all the way down when starting off and raised too fast getting on plane....operator error.

Tom

PS your boat/motor isn't fast mat be 62-65 mph Dry.

Tom

I don't know what you guys are talking about with operator error. I start out with it trimmed all the way down and I'm not touching the trim when it starts to cavitate. I've driven plenty of small boats. It's not operator error.

OK

Well, check the things suggested and make sure trimming in far enough.  How many bolt holes is the motor raised?