# Boat loosing traction



## Getsome (Sep 28, 2007)

I got a new to me boat just recently and like always, I'm working all the bugs out. Here is what I got: 2005 31' Pro Sport CC, twin Suzuki DF225. It has 4 blade 24 pitch props on it. One of the Suzuki's is brand new. First trip out to the bay in it, I noticed that when I throttled both engines up I was loosing grip and the RPM's went up. I brought it back in and figured that I had a hub spun on the props so I took them to Mr. Bill and had them re-cupped and the hubs checked. 

Bill said the cups were gone but the hubs were fine. I installed them back on the motors and went for another trip. Same exact problem with the newly cupped props. If I hold the RPM's high it will catch and plane off with no problem. The only time it happens is when I come out of the hole. What is happening?

The first trip out the boat was empty with no gear or people. Second trip it was loaded with ice, bait, people, and beer.


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## FishWalton (Jul 22, 2010)

That a big boat compared to my little river boat, but I had the same problem though. Went from a 9 pitch to 11 pitch and that solved the problem. Lost a little RPM but not enough to matter.


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## off route II (Sep 28, 2007)

what is your RPM at WOT?


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## PaulBoydenCustoms (Dec 3, 2008)

motors may be mounted too high


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## Chapman5011 (Mar 7, 2013)

They are cavitating. But not sure how to tell you what to do.


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## sailor (Oct 29, 2007)

PaulBoydenCustoms said:


> motors may be mounted too high


Sounds like this may be the problem. Did you ever get it up on plane and if so did it run correctly then?

With the motors in the down position, run a straight edge off the hull directly in front of the motors and see where it hits. Should be pretty close to this:


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## PaulBoydenCustoms (Dec 3, 2008)

sailor said:


> Sounds like this may be the problem. Did you ever get it up on plane and if so did it run correctly then?
> 
> With the motors in the down position, run a straight edge off the hull directly in front of the motors and see where it hits. Should be pretty close to this:



If the OP's boat is like mine with a stepped transom, they will need to be even higher than that. not sure of the correct formula, but im sure someone here has it


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## Getsome (Sep 28, 2007)

off route II said:


> what is your RPM at WOT?


WOT is 5,800 to 6,000. It will plane out but lots of cavitation in the process. It does fine once on plane. I think I misstated the prop pitch. I think they are 21P. When you open it up the RPM's shoot up to 5,800 until I back out of them. My buddy owns Blazer Boat Co so I called him today and he said it is a prop pitch problem. One of the engines is factory mounted and the other new one was installed exactly the same so I am assuming they are mounted correctly. My boat is at the trailer company getting belly boards installed so I don't have as much info until I get it back.


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## Getsome (Sep 28, 2007)

PaulBoydenCustoms said:


> If the OP's boat is like mine with a stepped transom, they will need to be even higher than that. not sure of the correct formula, but im sure someone here has it


Yes, I have a stepped transom.


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## off route II (Sep 28, 2007)

Getsome said:


> WOT is 5,800 to 6,000. It will plane out but lots of cavitation in the process. It does fine once on plane. I think I misstated the prop pitch. I think they are 21P. When you open it up the RPM's shoot up to 5,800 until I back out of them. My buddy owns Blazer Boat Co so I called him today and he said it is a prop pitch problem. One of the engines is factory mounted and the other new one was installed exactly the same so I am assuming they are mounted correctly. My boat is at the trailer company getting belly boards installed so I don't have as much info until I get it back.


 that's why I ask the question, I thought it was pitch. I had the same problem with my yellowfin, dropped from a 21 to a 19, both 4 blade. that fixed the problem and gave me a great hole shot. I think those motors should turn about 6500.


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## Getsome (Sep 28, 2007)

Here is the boat and engines. I'm thinking my buddy is right about the pitch. I just hate I re-cupped these if I'm not going to use them.


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## PaulBoydenCustoms (Dec 3, 2008)

if they were 19's id buy them from ya


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## RMS (Dec 9, 2008)

First of all, I assume you have the engines trimmed all the way down when taking off and trim tabs are not down much if any.

Hard to tell for sure with the engines trimmed up in the photos, but looks like the engines could be too high. First thing I would do is lower the engines, assuming there is room to do so. A photo of the engines lowered to where the cavitation plates are on the same plane as the bottom of the hull would tell us a lot more.


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## cheesegrits (Sep 18, 2013)

I agree with RMS, they look too high. This could be the angle of the pic of course. Post a pic like he says from the side with the ventilation plate lined up with the bottom of the hull. How far down can you drop them? Don't give up with the props until you try lowering them. One inch down can make a huge difference with hooking up. I think those motors have a 6000 rpm limiter on them.


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## X-Shark (Oct 3, 2007)

> One of the engines is factory mounted and the other new one was installed exactly the same so I am assuming they are mounted correctly.


That doesn't mean they are correct. Most mount them low and don't care. After all They are not paying the fuel bill and don't have to go back and lower them, if they cavitate....The Suzzy's will like being a Little lower throuh....It has to do with running the large 16in Dia. props.....You are doing that correct?


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## Getsome (Sep 28, 2007)

RMS said:


> First of all, I assume you have the engines trimmed all the way down when taking off and trim tabs are not down much if any.
> 
> Hard to tell for sure with the engines trimmed up in the photos, but looks like the engines could be too high. First thing I would do is lower the engines, assuming there is room to do so. A photo of the engines lowered to where the cavitation plates are on the same plane as the bottom of the hull would tell us a lot more.


Motors are always trimmed all the way down when I take off in any boat. I only use trim tabs for weight distribution control so I never have them down during takeoff.


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## Getsome (Sep 28, 2007)

cheesegrits said:


> I agree with RMS, they look too high. This could be the angle of the pic of course. Post a pic like he says from the side with the ventilation plate lined up with the bottom of the hull. How far down can you drop them? Don't give up with the props until you try lowering them. One inch down can make a huge difference with hooking up. I think those motors have a 6000 rpm limiter on them.


Engines are mounted in the last mounting holes. The only way to lower them would be jack plates.


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## Getsome (Sep 28, 2007)

X-Shark said:


> That doesn't mean they are correct. Most mount them low and don't care. After all They are not paying the fuel bill and don't have to go back and lower them, if they cavitate....The Suzzy's will like being a Little lower throuh....It has to do with running the large 16in Dia. props.....You are doing that correct?


I do understand that they could be incorrect. I just find it hard to believe that being the 4th owner nobody would have addressed it before me. Especially the first owner after he got it new. I'm almost sure they are 16'' diameter props. I will confirm. 

I do believe you are right about the rev limiters at 6,000.


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## Getsome (Sep 28, 2007)

Ok, here is the theory that Barry and Bill have come up with at the prop shop. The thrust washers are the wrong ones for the props. They are holding the props too far out of the lower unit allowing exhaust to escape between the prop and foot. This is creating a air pocket around the prop. I won't know until Sunday when I get it back on the water. It sounds feasible I guess. What do y'all think?


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## Mac1528 (Mar 24, 2012)

If that exhaust is coming out before the prop....your trying to push that big feller with air instead of water! Makes sense to me.


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## X-Shark (Oct 3, 2007)

> I just find it hard to believe that being the 4th owner nobody would have addressed it before me. Especially the first owner after he got it new.


You need to put that out of your mind.... People in general are lazy and uneducated.

If those owners just wanted to go fishing and the boat got them there.....That's all they cared about. Then there is the Big money experiment of buying props. The money part is the deterrent. 

I had to get props shipped to me from Prop Gods....The local 2 prop shops don't have 16in props that the Suzzy's need to run. Power Tech props are not in the high echelon of propellers.


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## Pomponius Maximus (Apr 12, 2013)

I notice your props have holes drilled near the front edge of the blades,these are prop ventilation ports used on heavy rigs as well as bass boats and ski rigs,...it helps get the rpms up and get the boat moving.

Plug two holes on each prop and try again....may need to plug all of them......your prop guy should be privy to these vent holes.....they are usually done by prop guys ,.not the factory. Some came with plastic plugs to be used or not as required.


Trim it High and Let it Fly....! ! !


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## Mac1528 (Mar 24, 2012)

Pomponius Maximus said:


> I notice your props have holes drilled near the front edge of the blades.......


Man....you got eyes like a hawk!! I know I'm old but I still can't see that.


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## RMS (Dec 9, 2008)

Pomponius Maximus said:


> I notice your props have holes drilled near the front edge of the blades,these are prop ventilation ports used on heavy rigs as well as bass boats and ski rigs,...it helps get the rpms up and get the boat moving.
> 
> Plug two holes on each prop and try again....may need to plug all of them......your prop guy should be privy to these vent holes.....they are usually done by prop guys ,.not the factory. Some came with plastic plugs to be used or not as required.
> 
> ...


I didn't notice the holes either until Pomp pointed them out.
To add a bit more to Pomp's comments, which are spot on, the holes and the thrust washer spacing are designed to intentionally introduce exhaust gases around the hub during take-off to allow a controlled amount of cavitation so the rpms can get up to max torque (efficiency) quickly.

As the boat speed increases, the force of water pressure against the lower unit and prop hub overcome the exhaust pressure and reduces or eliminates the "venting" once up on plane. 

As mentioned, some props come with holes drilled and sets of plastic bushings of varying size to "tune" the level of venting for each individual application.

Sounds like you may be getting more venting than you want.

If I were in your situation, I would consider first plugging all the holes completely perhaps with JB weld or epoxy, and test the result. It would cost nothing but perhaps an hour of your time. 

If the change is too great, you could start gradually drilling out the plugs one bit size at a time until you get the desired balance.

On the other hand, if completely plugging the holes is not sufficient, you could then address the thrust washer spacing, which will probably cost some $.


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## Pomponius Maximus (Apr 12, 2013)

Uh.......not sure if I got eyes like a hawk or not.......took another look...

those look like short shaft bass boat motors.....you need 25 inch shaft motors.......where did you buy the boat ?.....whats its story ? ?.....

did someone remotor this boat.......things could get sticky if you have been mislead.............lied to..........

hope it works out............


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## wld1985 (Oct 2, 2007)

Mike it sounds to me like, ya just need another newer boat.. And hand me over the keys to that piece that is giving ya problems.. I might be able to put fuel in it...

Not sure on any of the problems here, Give it ashot and see if taking the ""Spacers out"" works or not.. The Motors do look kinda short though..


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## Getsome (Sep 28, 2007)

RMS said:


> I didn't notice the holes either until Pomp pointed them out.
> To add a bit more to Pomp's comments, which are spot on, the holes and the thrust washer spacing are designed to intentionally introduce exhaust gases around the hub during take-off to allow a controlled amount of cavitation so the rpms can get up to max torque (efficiency) quickly.
> 
> As the boat speed increases, the force of water pressure against the lower unit and prop hub overcome the exhaust pressure and reduces or eliminates the "venting" once up on plane.
> ...


This is the final conclusion on the props. After taking the thrust washers to the Prop Shop, they determined they are the right washers . We put spot putty in all the holes to see if that makes a difference. The engines are 25'' shafts. I put a 4' level from the cavitation plate to the keel to see how low the motors are. On the outside of the engines the plate is 1.5'' above the keel but on the inside between the motors where it V's, it's closer to 3'' higher than the keel.

I am going out Sunday morning, I will update this post to see if closing the holes off works.


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## Getsome (Sep 28, 2007)

Pomponius Maximus said:


> Uh.......not sure if I got eyes like a hawk or not.......took another look...
> 
> those look like short shaft bass boat motors.....you need 25 inch shaft motors.......where did you buy the boat ?.....whats its story ? ?.....
> 
> ...


I bought it local from a guy that needed the money. The starboard motor was blown when I bought it. I had a new Suzuki installed on on starboard but the port is still the 2005 original. I knew going into it that there would be bugs to work out and fine tuning to do. I have all new pumps, lights, trailer, and upholstery. At this point I'm $45K deep but I'm, the kind of guy that likes everything working when I go fishing.


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## X-Shark (Oct 3, 2007)

For the guys that thought the motors were short.

This is what happens when not concise pix's are taken. No Side shots with straight edge.

Pix's of props not showing good detail of the vent holes or not showing them well.


Keep this in mind when asking questions. Detailed pix's are imperative to getting educated answers to those questions.


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## Mac1528 (Mar 24, 2012)

Getsome said:


> I am going out Sunday morning, I will update this post to see if closing the holes off works.


So???? What's the outcome?


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## Getsome (Sep 28, 2007)

Mac1528 said:


> So???? What's the outcome?


Sorry, I forgot to post. The putty worked that morning. By noon, port engine started back to over reving. Got home and the putty had come out of the port prop. Conclusion: Weld the holes up in the props. It does have me wondering if the props are doing what they are intended to do like a stall converter in a transmission. I've just never had a boat with props configured this way so I would not know.


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## Mac1528 (Mar 24, 2012)

Thanks for the update. I have had several props reworked but have never seen one with holes in it. RMSs explanation does have some merit but I'm not in that league. Thanks again!


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## X-Shark (Oct 3, 2007)

You know they make plastic buttons to pop in those holes....Right?


http://www.amazon.com/Mercury-Performance-System-Solid-Plugs/dp/B003907QOG


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## Getsome (Sep 28, 2007)

X-Shark said:


> You know they make plastic buttons to pop in those holes....Right?
> 
> 
> http://www.amazon.com/Mercury-Performance-System-Solid-Plugs/dp/B003907QOG


I have heard of this.


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## RMS (Dec 9, 2008)

X-Shark said:


> You know they make plastic buttons to pop in those holes....Right?
> 
> 
> http://www.amazon.com/Mercury-Performance-System-Solid-Plugs/dp/B003907QOG


They are unlikely to fit unless he has Mercury props with factory vent holes.


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