Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

[Lakes84]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

A recent test. I dunno...Don't shoot the messenger!


To show the dramatic effect cleanliness plays, a boat was left anchored in salt water for 40 days. The running tests were made with a 35 HP engine which was removed from the boat after each test. A three-man load was used.

Speed:

At beginning of test . . . 25.0 mph (40 km/h)
After 10 days in water. . 21.5 mph (35 km/h)
After 20 days in water. . 18.5 mph (30 km/h)
After 40 days in water. . 13.0 mph (21 km/h)

 

[smokeonthewater]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

right on guys but that isn't the problem he is having.... he is getting respectable speed but his RPM's are spiking..... slow heavy draggy boats LUG.... they don't (in my experience) over rev and THEN lose speed

 

[Lakes84]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

I have to believe this is a prop issue, just because he can recreate it at different throttle levels and different trim angles. A lot of questions would be answered if you just tried another prop and got back to us. Not sure if you should go down in pitch or up, considering the symptoms, but it would eliminate a lot of the guess work.

Joe

 

[QC]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

We're talking pitch changes? Why?

The speculation has been that prop design, prop condition or the bottom is causing ventilation.

Orrrr, the prop hub is spun, or prop coupler is spun. These seem unlikely to me as he can make the problem go away. Possible? Yes. Probable? I don't think so. But that's just me and I have not been in a Holiday Inn Express in 4 or 5 days . . .

 

[Lakes84]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

Well, when I was having prop issues I couldn't explain with my new Ranger Reata, that was the easiest thing to do. You're right, maybe it's not a pitch change, just a prop change, heck why not? no one else has came up with a definitive answer over the internet. It's cheaper than taking it to a mechanic I would think. If in fact he can't diagnose it being a prop hub or a coupler

 

[Captain Gecko]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

Thanks again guys, I'm going to take her out again this weekend, will report back and see if I can get some more answers/observations. Might not be able to get a new prop on just yet though (still in the water, no trailer).

 

[smokeonthewater]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

It's EASY to change the prop in the water..... they make floating prop wrenches for a reason..... honestly, If you don't have a spare prop and a wrench on board you NEED to buy them asap....

 

[oops!]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

I still think this is a vent/cav issue.

If the coupler was toast....it would be consistent loss thru the power band.....especially at hole shot. Getting worse at each wot till no more forward. This accompanied by the horrible feeling that "something is wrong"

Spun hub ?.....same ......till there was no more hub......this, again, accompanied by the horrible feeling that "something is wrong"

Hull growth?....possibly some.....but not all......but it can be a factor. worth checking.

waterlogged?......again....consistent loss thru rpm band.....but will not cause slip at wot....but rather.....low rpm at wot.


so.......we are back to cav/vent.

btw.....to check for a waterlogged hull......get it on a trailer and weigh it against manufacturers specs....there should be no reason for change.

 

[lime4x4]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

I'd go with a prop hub. Had the same thing happen to me this summer. Boat would work great then all of sudden it would lose forward motion then the rpm's would flare. Back off throttle then back on the throttle after a few minutes the same thing started to happen again. Checked prop/hub while in the water. I could turn the engine with the prop.After a couple of miles of it doing this it finally destroyed the hub. Actualy the hub melted from all the slipping

 

[Lakes84]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

btw.....to check for a waterlogged hull......get it on a trailer and weigh it against manufacturers specs....there should be no reason for change.

Hey! I was going to post that same exact thing last night, but thought it couldn't reasonably be done. I'm glad someone else thought of it. I was going to add make sure you take the weight of any add ons into account, including your gas and other fluids, as manufacturers specs, I do believe are dry weight only. Someone please correct me if I'm wrong.

Joe

 

[chriscraft254]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

Most boats weight specs are empty with no motors. Basically a hull weight. Easiest way to weigh the boat is take it to the landfill and weigh trailer and boat and subtract trailer weight. Or take the trailer there first, then with the boat.

Hey! I was going to post that same exact thing last night, but thought it couldn't reasonably be done. I'm glad someone else thought of it. I was going to add make sure you take the weight of any add ons into account, including your gas and other fluids, as manufacturers specs, I do believe are dry weight only. Someone please correct me if I'm wrong.

Joe

 

[Captain Gecko]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

Hi all,

Sorry for the late reply/follow-up. It's been busy!

I did take the boat out for a few runs before winterizing and I inspected a few things. The bottom of the hull is actually quite clean, very minimal build-up. So I don't think that is the primary issue. With the right combo of outdrive trim and trim tab settings, I was able to cruise at full throttle without the issue presenting itself. As soon as I tried to lower the trim a bit, it happened again.

Now that the boat is out of the water and on my trailer, I had a good look at the prop. See pics below. Although it's worn-looking, there does not appear to be any damage to it. I will likely buy another in the spring anyway and try that.

1 - I did notice that there is some sort of flex hose that is sheared off. I'll need to replace it, see pic below. Any ideas what this is? The pic is taken from underneath the outdrive, looking up.

2 - There appears to be some sort of corroded alloy fin directly above the prop. Is this supposed to corrode like this?

And yes, I seriously need to clean the outdrive.

 

[smokeonthewater]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

That "flex hose" is your exhaust bellows... it isn't important at all but it's condition is likely a warning of the condition of the other bellows and THEY will sink your boat when they tear..... Get them replaced.... The "corroded alloy fin" is your steering trim tab and is also a sacrificial anode... yes it IS supposed to look like that.... that means it is doing it's job.... When it starts to corrode so bad that it starts dispensing, replace it.

 

[Captain Gecko]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

That "flex hose" is your exhaust bellows... it isn't important at all but it's condition is likely a warning of the condition of the other bellows and THEY will sink your boat when they tear..... Get them replaced.... The "corroded alloy fin" is your steering trim tab and is also a sacrificial anode... yes it IS supposed to look like that.... that means it is doing it's job.... When it starts to corrode so bad that it starts dispensing, replace it.

Great info, thank you.

 

[Bondo]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

I had a good look at the prop. See pics below. Although it's worn-looking, there does not appear to be any damage to it. I will likely buy another in the spring anyway and try that.

1 - I did notice that there is some sort of flex hose that is sheared off. I'll need to replace it, see pic below. Any ideas what this is? The pic is taken from underneath the outdrive, looking up.

Ayuh,... Like Smoke said, yer exhaust bellows is ripped,...
In itself it ain't so bad, but it tells ya the rest of the bellows are probably junk too...

That prop is at best a Spare,...
It's pretty beat, 'n the flare ring is missing...
That alone could be yer ventilation problem...

 

[TilliamWe]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

...
It's pretty beat, 'n the flare ring is missing...
That alone could be yer ventilation problem...

It almost looks like the prop is bolted on backwards! You need a new prop, for sure.

 

[smokeonthewater]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

Good catch bondo..... It looked goofy to me but I didn't notice why lol..... Agree, prop is toast and likely that's the prob

btw .. auto complete got me on my last post.... I meant that when the fin starts disapearing you need to replace it LOL

 

[Captain Gecko]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

Thanks again, learning a lot...

Looks like I have some Spring projects!

On the plus side, I pulled all the carpets out and cleaned her out getting ready for winterization. The whole floor and hull seems rock solid. I pulled the floor panels and it looks just as solid underneath. Stringers(?) appear to be plywood coated in fiberglass, they are in good shape. Gas tank is huge, aluminum it looks like.

I plan to clean it up again come Spring, perhaps paint the hull partially, replace a few seats and of course get the motor tuned and inspected. Will replace the prop, bellows exhaust and anything else DIY myself.

Cheers,
Chris

 

[chriscraft254]

Re: Boat, prop or engine issue? 24' cuddy loses traction at high speed 5.7 merc a1

Ayuh,... Like Smoke said, yer exhaust bellows is ripped,...
In itself it ain't so bad, but it tells ya the rest of the bellows are probably junk too...

That prop is at best a Spare,...
It's pretty beat, 'n the flare ring is missing...
That alone could be yer ventilation problem...

Good catch on the flare ring. That indeed could be causing some weird issues with cavitation or ventilation I would think.