Wee lassie in need of advice,

[sexy sue]

Pleese Guys, I have taken on my Dads boat,
with the help of my brother who is a mechanic, been on the safety courses and we are out to sea,
not too far tho and only on calm sunny days, its great! me and my girly freinds are loving it, especially back at the cruise club and on the marina with all you handsome boaty guys! any way i hope that is enough flattery for you,
to the point fellas, when i get to about 3100rpm and the boat is on the plane, it develops a shuddery juddery vibration thing, ease back to 2600rpm and it stops,, my boat is a 25ft Sealine with a mercruiser 485 engine and alpha drive, any ideas fellas on which direction I should point my little bro in? och aye, many thanks

 

[Bondo]

Re: Wee lassie in need of advice,

Ayuh,... Hi Sue,.. Welcome Aboard...

What kinda shape is the Prop in,..?? Dinged up, it could cause the vibrations...
Has the boat been Properly Maintained,..??
Head up to the Adults Only section at the top of this forum,...
There's Factory Manuals,+ a Boatload of Great Info up there....

 

[a70eliminator]

Re: Wee lassie in need of advice,

Have you tried to throttle up to say 4000 through the vibration, I ask to rule out an ignition related misfire, because if so your not going to achieve max RPM's. The drive is the most probable culprit, bad u-joint (vibrate in a slow turn?) bent propshaft (dial indicator) or like already mentioned damaged prop (easy fix) I almost forgot to mention, that's a pretty big boat I'm guessing it's moored, I've heard about garbage like plastic baggies, fishing line, string, seaweed, stuff like that getting wrapped up in the propshaft.

 

[futz]

Re: Wee lassie in need of advice,

This boat stay in the water all the time? If yes i would first thing is have it pulled out of the water and the drive and hull inspected for barnicals. Probably spelled wrong, any growth on the hull and drive.

Same time check the prop.

 

[Haut Medoc]

Re: Wee lassie in need of advice,

I would check the prop as well....
25 feet of boat on a 485, that engine has to be working HARD....
I would think the prop would need to be in tip top shape....

 

[sexy sue]

Re: Wee lassie in need of advice,

OOh you lovely boys! thank you so much for coming back so quickly with your replies, i never expected that,

Ok, Mr Bondo, yes the boat has been properly serviced and maintained my dad was meticulous, Jimmy said the prop was in good order without dings or damage but he did spray the outdrive with international "prop o drev" antifoul at least twice before the start of summer, and the bellows were done two seasons ago,

Mr Eliminator, no i am too scared to open the throttle right up ( I am a Girl) once it starts juddering, will it do any damage? how will i know if it is ignition related? do you mean if it wont reach top revs? Jimmy said it shoud max at 4600, correct?
The boat does stay in the sea for 5 months but its clean and without any growth or barnacles,

Mr Medoc, she is just under 25ft, weighs 2.4 tons and cruises at 18 knots, up on the plane at 3400 rpm max speed at 4400 24 knots these are all my dads notes, what is the general feeling about 485 engine (dont worry you wont hurt my feelings) are you suggesting that the wee engine is not man enough for the job?
Thanks lads for your help thus far young Jimmy will be a busy boy in the morning, xx

 

[Haut Medoc]

Re: Wee lassie in need of advice,

The 485 is a mutation of the 170, & it would not be my first choice for an engine....
They have their quirky issues, but they deliver alot of horse power for their size & weight....
That said, a 4 cyl engine on a 25 footer that weighs 2400kg, is alot to ask of it....
I would say the boat is underpowered......
Shuddering sounds like a prop, bent prop shaft, or alignment issue....
You cannot always visually detect a imbalanced prop....
Will it power through the shudder or does it get worse?...
The cheapest way to test it would be to put on your spare prop...
If you don't have one, you should....

 

[jtybt]

Re: Wee lassie in need of advice,

Sexy Sue, Huh!

A 25 sealine(5000 lbs)is a lot of boat for a 4 cylinder. I really doubt it gets to 25 knts...but ya never know.

A 4 cylinder just ain't going anywhere if it's a problem with plugs, firing order or anything else ignition related.

Has to something in the drive line. Re-check prop carefully for any sign it could have deflected in sand or something soft so as not to leave a hard mark or ding. Look at the skeg(bottom fin) for signs, too. Pull the boat and check the prop shaft, too as suggested.

 

[a70eliminator]

Re: Wee lassie in need of advice,

What I meant about powering up is that ignition spark problems would cause a shuddering shaking engine, and if thats the case your not going to achieve max RPM's. If you can get to max RPM's then it's probably not an engine problem. I don't think it could hurt to just wring it one time to see, but then again I don't know how bad your shake is, maybe it's not a good idea.

 

[sexy sue]

Re: Wee lassie in need of advice,

Ok thank you for the explaination, so how about if i try to rev it when it is on the mooring but not in gear? if she builds up to 4500 as she should can i rule out engine problem? thank ee

 

[sexy sue]

Re: Wee lassie in need of advice,

OK guys, thank you for all your advice, Me and my girlfreinds are going to drag Jimmy down to the boat today to make the checks that you have suggested, we will let you know.

 

[jtybt]

Re: Wee lassie in need of advice,

...and reving an engine in neutral will tell you very little of it's condition. You could probably pull two or three plugs and still rev it to 4000 RPM.

 

[proxyx]

Re: Wee lassie in need of advice,

the boat will shudder if ignition misfires/misses as well, check ignition and spark plug wires
you CAN momentarily rev up the engine to ~4000, has to be warm though and in water. High RPM under load is the way to go though, as pointed out.

 

[sexy sue]

Re: Wee lassie in need of advice,

Just got back from our boat, weel fellas, the boat revs just fine ,no misfiring or hesitation, at the last service it had new plugs, leads cap thing and points,
it was far too windy today to go out and test it on the sea, however we got it out and looked at the prop, but it was as always, at least no evidence of damage,
so i guess i will have to get one flown over to test and keep it as a spare if its not prop problems,
the boat comes out in 4 weeks for the winter so i suppose it is time for a strip down of the drive, Jimmy is gonna love that!
if it is the case that we can get to it in the week and find that she will drive through the wobble and go to max revs, what does that indicate or mean? thanx for your time guys.x

 

[Bondo]

Re: Wee lassie in need of advice,

if it is the case that we can get to it in the week and find that she will drive through the wobble and go to max revs, what does that indicate or mean? thanx for your time guys.

Ayuh,... It means something is outa Wack,+ the vibrations cancel out after a certain rpms....
You'll Still have to diagnose the Why's,+ What's of it....

Is this something that Just started happening, or something that You just discovered,..??
Was anything done to the barge Just before this started,..??
As long as the motor is runnin' smoothly,... There's not alot you can do til it's on the Hard....

 

[sexy sue]

Re: Wee lassie in need of advice,

I only noticed it a few weeks ago, but Jim thinks it may have been doing it for some time, possibly started after the head gasket was replaced last season but he cant be sure,i drove the boat a lot last year and never noticed it, poor Jimmy is really scratching his head, how is he ever going to find out if it is the engine or the drive side, the engine starts runs sweet, has 148psi in the cylinders( jim told me that) he has a little clock thingy to test it, we dont seem to get any vibrate in slow turn either, will try and give her a blast this week if the weather bucks up, tatty bye for now,

 

[sexy sue]

Re: Wee lassie in need of advice,

Yippeee! Nothing wrong with it, took the boat out today and caned it big time, 4 on board and we stoked it, slow then fast then stop then ripped her up to max, then down again, Garmin said 24.7 knts, as always up on the plane at 3400, we did this for 2 hours wasted loads of fuel, all in all a thorough testing, and the conclusion: first time we have had flat sea for 10 weeks, IT WAS THE WAVES! no judder, no shudder, no vibration, fast and smooth just how we like it! many thanks for your input fellas, well what did you expect? I am a girl!
bye for now xx close thread

 

[jtybt]

Re: Wee lassie in need of advice,

Nice Sue!

Next time out, do a WOT run (Wide Open Throttle) to see what your max RPM is. The 485 has a WOT of 4400-4800 RPM.