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

[Captain Gecko]

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

Thanks again guys, great info all around. I've only had a cursory look at the hull, getting too chilly here to dive in. I'd say it has a medium growth of fine-haired green algae and associated grime and gunk? So I am guessing this is causing some drag as well, perhaps relating to the issue. However it seems like 'check for spun prop' is my first test, per the mark the hub method. Since it's end of season here and I'll be pulling her out soon (sniff), I'll give her a full cleaning and checkup at that point as well.

This forum has already been invaluable to me - great community!

Chris

 

[TilliamWe]

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

If I am wrong, please do elaborate! I am always open to learning more about different subjects.

Start learning here:

This is growth in the Illinois River, at Peoria, in about 3 weeks in July! So you can try to point out your "qualifying" statements all you want, but the fact is LESS than one season's growth can indeed be enough to adversly affect a boat's performance. You can not make a blanket statement that one seaon's growth can't cause problems, because it is not true. I just proved it with 2 photos. Unfortunately I also proved it with 5 tulipped valves on a Vortec 5.7!

Gecko, the growth probably is NOT the specific cause of your problem, but it can cause other problems (valve damage as I noted above). Any boat that is slipped in the water, should have bottom paint (with an epoxy barrier coat applied first). To minimize growth and to protect the gelcoat from blisters.

 

[chriscraft254]

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

Lmao, you just proved my point! Did you read what I wrote? Also, the pics your showing is exactly what I had said, the growth will start toward the sides. The underneath part vary rarely has alot of growth unless the boat sits without use! Its a shame to see you let your boat get that dirty. When I take mine out, I simply stop at the beach and scrub the sides down. Takes all of about 5 minutes. You are right, you should have the bottom painted if you will be leaving it in the water for extended periods of time.

Who told you the algae ruined your valves? That cracks me up! :facepalm: Gecko, sorry about the derail. Was just trying to help.

Start learning here:

This is growth in the Illinois River, at Peoria, in about 3 weeks in July! So you can try to point out your "qualifying" statements all you want, but the fact is LESS than one season's growth can indeed be enough to adversly affect a boat's performance. You can not make a blanket statement that one seaon's growth can't cause problems, because it is not true. I just proved it with 2 photos. Unfortunately I also proved it with 5 tulipped valves on a Vortec 5.7!

Gecko, the growth probably is NOT the specific cause of your problem, but it can cause other problems (valve damage as I noted above). Any boat that is slipped in the water, should have bottom paint (with an epoxy barrier coat applied first). To minimize growth and to protect the gelcoat from blisters.

 

[25thmustang]

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

One season in my fresh water slip, using the boat once a week, sometimes once every other week and it never has any growth. A little bit of brown staining along the portion of the hull just above the top of the bottom paint, but no growth.

 

[QC]

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

Who told you the algae ruined your valves? That cracks me up! :facepalm: Gecko, sorry about the derail. Was just trying to help.

His point was that the increased load caused a lug condition, and that's why he tuliped valves. Chris, others experiences here are valid too

 

[ezmobee]

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

Maybe, but spun hubs RARELY can make speed too. Possible, but not probable. A seasons worth of growth is not significant? Never heard that before . . .

I had one that only slipped if you floored it.

 

[QC]

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

I had one that only slipped if you floored it.

Agree, but also make 35 MPH? In a heavy ride? They happen for sure, but usually they slip when you hammer the throttle and won't make decent speed. Speed = load as much as hammering the throttle does, although you could make an interesting peak torque argument here. Say it slips at 242.5 lb/ft and above, and say the motor is capable of 265 lb/ft. at Peak torque, but generated only 200 lb/ft @ WOT RPM and there it wouldn't slip. Possible, but again unlikely.

I am not saying this isn't a spun hub. And maybe I am as big a problem as others in considering my thoughts as correct. The proper thing to do with any problem is to diagnose by data collection and elimination of issues one at a time. Prop hub scribe is the easy way to check for that, and definitive. If the prop was swapped and it fixed it, many would say "spun hub proof" and I would say "no, now you know nothing. Could've been a spun hub, or prop damage, or prop design. Now you don't know". Yes, you need a spare, but that's another issue.

To me this acts just like ventilation as he can make it go away with trim adjustments. Not just throttle. Yes, that can change the load on the shaft and hence the hub, but it is not definitive. This does not mean that the hub is good. If the scribe method shows the hub is good then I suspect bottom growth, or prop damage (could be minor). The bottom growth can change the way water is hitting the propeller at different speeds, just like a transducer can. This doesn't mean that bottom growth is the definitive answer.

Slight propeller damage or a bad casting can cause this too. This is why you make one change at a time, so that you can be confident of what actually is causing it. Swapping the prop introduces three possibilities, hub, prop design and damage. Which one are you going to blame if the swap fixes it? Ultimately the boat would run and the OP would be happy. But inquiring minds need to know and the rest of us would be left to fight over who was "right" . . . Can't have that :facepalm:

Oh, oh, could be all of above, or none of them too Could be mangled tabs, or a mangled AV plate, or even Spinner's Little Buddies (hey big guy)

 

[smokeonthewater]

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

I find it HIGHLY unlikely that the slight algae pictured above lugged the engine enough to damage it... If that were the case towing tubes and skiers would be a death sentence... Anyhow on the O/P's issue.... I think this is a case of cavitation due to a damaged prop and not ventilation... I also doubt that this is a hub as trimming up and tabbing down (and as stated by the O/P reducing rpm's) slows the boat and increases the load on the drive train.... If the hub were slipping it I doubt it would stop in these conditions.

Honestly the FIRST step is to inspect the engine compartment around the back of the engine and on the inside of the transom for nasty black goop and or bits of rubber. (spun coupler).... If none then get a little wet and inspect the prop. Just back unto a slip and trim all the way up... Make CERTAIN that the boat is tied fast so that it can't move and smash you against the dock....you should be able to reach the prop from the dock.... If it's in good shape then move on to the hub slip check as noted above.....

 

[ezmobee]

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

Nerd.

 

[QC]

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

Nerd.

Funny, Mr's QC says the same thing . . .

 

[QC]

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

Honestly the FIRST step is to inspect the engine compartment around the back of the engine and on the inside of the transom for nasty black goop and or bits of rubber. (spun hub)....

Spun or burnt "Coupler" . . .

 

[smokeonthewater]

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

WHOOPS.... yeah coupler...... UGH

 

[Captain Gecko]

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

Lol, thanks all. You guys know each other a bit already I take it?

I will follow the great advice here and start sleuthing. I don't have anywhere near the growth in that pic posted earlier.

Will try scribing the hub and start there. Didn't notice any nasty goop from spinning my coupler...wait that came out wrong...I mean a spun coupler, but I will have a closer look at the engine compartment.

Supposed to have some nice weather this weekend, may as well take a dip!

Cheers,
Chris

 

[Philster]

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

A serious problem usually has more than one contributing factor. We tend to look for a single cause, but should look for multiple issues in some cases.

I've been on a couple of water-logged boats that did exactly what the OP described. They were stern heavy and wet inside -- they just seemed to be most saturated in the rear or presented themselves that way, and the prop couldn't take it anymore at higher speeds. The stern wasn't coming out of the water as much as it should. The prop simply could not lift it anymore. The telltale signs were:

>Not getting full RPM
>Losing top end
>Prop seems to lose bite... or simply won't hold when trimmed up as much as it used to be

^The first two alone = prop issues, power issues, mech issues. Toss in number three... and well...

A water-logged hull might be enough alone, or it not be enough, because boat engines with good power/torque can mask it a bit. Throw in some hull growth and a motor (maybe) that is starting to get worn/tired, and at the upper ends of RPM and speed there is no more trim to offer and/or the prop just seems to lost it, because it can't lift what it used too. Having a ton of water in the hull will make the prop lose it at upper RPMs. It just will.

So, sure, check the outside of the hull, but check the inside, too. I got a nickel that says she's waterlogged. Oh, and if the outside of the boat got funky because someone didn't prevent it, odds are good the inside got funky.

.

 

[Captain Gecko]

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

Philster - how do I check the hull for being water-logged?

The boat was well-maintained, very clean. New outdrive a few years ago, new canvas, etc. She was winterized each year, etc. Deck is strong everywhere. When I pull the deck panels, compartments are dry underneath.

So where would I look?

 

[Philster]

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

I reread the opening post, and I have to say, "with the trim tabs down it helps" concerns me as well. I missed that the first time.

Alright... if she is as$ heavy, the trim tabs will help get the as$ heavy stern up, so you mask the issue a bit, but there is a breaking point between that am't of traction the prop has and the am't of weight it needs to carry/lift.

Where to look to see if the boat is water logged with wet foam? Depends on the model. I don't know enough about yours to know where to look. Someone here might recommend a core sample, or you might be able to check from hatches and such.

I think there are three variables that need to be eliminated here:

1) is the hull waterlogged?
2) is the prop the right type (your boat might need a better stern lifting prop)?
3) is the hull as clean as can be?

Just to be clear: WOT runs are full-throttle runs, with tabs up as far as possible.

 

[QC]

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

Where to look to see if the boat is water logged with wet foam? Depends on the model. I don't know enough about yours to know where to look.

Very rare for ANY 20+ footer to have foam anywhere . . . Flotation is mandated 20' and below. Somebody please chime in, but I don't there's any real chance that there is foam at all.

 

[smokeonthewater]

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

I can't say that it is impossible but I just don't see this being a stern heavy problem..... His symptoms don't support it.... He makes no complaints about holeshot and his trim settings are opposite of what I would expect.... OTOH I've never experienced a boat that cavitates or ventilates when trimmed down but not when trimmed up.....

I still think this is going to be a mechanical issue..... torn up prop, spun hub or spun coupler

 

[chriscraft254]

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

There was a federal boating safety act instilled in 1971. There was a period of time given to boat builders to adhere to the act. It was mandated in 1977 for boats 20 ft and under to have positive floatation. There were many boats older than that that did have floatation but it was just up to the manufacturer and nothing was really regulated. I had a 1977 19' mako that was foam filled and also 1976 15' mako that was foam filled. Both of those boats had floatation all the way up to the gunnel caps. Some of the older grady's have foam,some don't. The foam in these WA are usually just in below the deck, nothing in the gunnels. So there is a chance that there is foam in there and if there is foam, it is surely saturated being as old as it is.

Op, keep us posted, we all look forward to hearing what you find is the issue.

Very rare for ANY 20+ footer to have foam anywhere . . . Flotation is mandated 20' and below. Somebody please chime in, but I don't there's any real chance that there is foam at all.

 

[Philster]

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

Waterlogged boats can have fine hole shots (worse than if they were lighter, but they still get going), but the engine/prop can't get to full speed. If the hull isn't lifting out of the water as far as it should, the extra resistance (drag from too much wetted hull), combined with extra water weight results in falling short of peak RPM range and speed. If the whole shebang is riding funny (too a$s heavy), the prop is down there in that mess and caught in the soup or falling because it can't lift the stern/boat.