The great gearbox swop!

Solitaire

Solitaire

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Well, work started today. Some may recall the Peters liquidation auction and we managed to "win" a pair of VP Hydraulic gearboxes. New, unused, boxed and some may say that we got them for a song! Well we did! Anyway, on collecting them it became obvious that we would have some work to do in terms of props. Motala's existing gearboxes were 1.93:1. The new gearboxes are 2.68:1. Was it going to be possible to re-prop. Initially it looked as if it might be a problem, but in consultation with Lancing Marine we came up with a solution and our new props were delivered a few weeks ago in preparation.

Here is a pic of the new prop alongside the existing 5 bladed prop. Tomorrow the old gearboxes come out and by Monday we hope to be all installed. Keep your fingers X'd!





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Looks a big difference in size!! The five bladers would be queiter.

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Yes my thoughts too. And how much hull clearance is there?
 
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Looks a big difference in size!! The five bladers would be queiter.

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Old prop size was 17 new ones are 20 x 25. It has all been worked out (hopefully) and we are aware of the increase in noise. But we were never pulling max revs on the engines with the old set up after we replaced the engines. Anyway, time and sea trials next week will tell!

As to distance from the hull, that was of prime concern when we knew what the ratios of the gearboxes were. But all was worked with Lancing Marine over a period of months and consultation with Storebro in Sweden who were very helpful.
 
I read 2 inches clearance between blade tip and hull should be a minimum.

With then running slower the torque will be higher, looks like a skinny shaft to me!

ETA - props seem to be a bit of a black art but Mike Bellamy knows his stuff.
 
Re:There in!

Well they are in - all went to plan and we also changed the seals behind the fly wheels while we had the boxes off. So far so good. A few pix of what went on today.

Out with the old!

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The bell housings ready to accept the new boxes.
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One of the new boxes.

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Col greasing the new seals

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Col getting ready with a bit of precision equipment

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How tight?

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[--word removed--] they are heavy!

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Done it!

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NB!
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Both in and bolted up
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Close up
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The next task is to fit the couplings and the props - will see more tomorrow. But if it all goes as well as it has today then we are ahead of schedule.
 
Re:There in!

Hmm nice boxes ive done this before too, shame poor old col never gets to enjoy his own boat as hes always on other peoples boats! I know how he feels.

Nice job, best get those old ms boxes out the way, though scrap is down at the moment.
 
Re:There in!

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shame poor old col never gets to enjoy his own boat as hes always on other peoples boats! I know how he feels.

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Ah, now that's where you are wrong. I was aboard Col's boat this morning and heard his engines fire up. All nicely done with S/S bolts etc. Plus all the other stuff he has done, including now having separate gears and throttle set up. He's a bit disapointed though as he needs different props as he can only get 35 knots he reckons. Needs C6s not the C5s he currently has.

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Nice job, best get those old ms boxes out the way, though scrap is down at the moment.

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Once we have done all the sea trials they will be on the market. They work fine, just that when you get a brace of gearboxes, still in their wrappers, never been registered for warranty for, well lets say a very very very very good price what is a man to do? /forums/images/graemlins/laugh.gif
 
Re:There in!

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ang on there no good there a different green............................will never work

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/forums/images/graemlins/wink.gif
 
Re:There in!

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He's a bit disapointed though as he needs different props as he can only get 35 knots he reckons. Needs C6s not the C5s he currently has.

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Oh, I shouldn't worry. This is Col after all. Those C5's should start to fall off as soon as he clears the Hamble, leaving room for some new ones.
 
How many man hours did it take , was the idea just to loose the clonk while changing gear or do hydraulic boxes have other advantages ?


Now what I am sure is a silly question but what I really wanted to know

If the pitch of a prop can be changed to such a large degree why do they make so many different gear ratios ?

Are there any advantages/disadvantages to small gear ratio--------large prop pitch.


Great report and interesting read thanks /forums/images/graemlins/smile.gif
 
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How many man hours did it take , was the idea just to loose the clonk while changing gear or do hydraulic boxes have other advantages ?

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We didn't really time the change. But as the engine room access is so good it was not really that long. The shafts were dismantled from the gearboxes and that took maybe 15 mins. The gearboaxes unbolted and the cooling pipes etc taken off, we also decided to replace the stuffing boxes with the newer type so no longer have the stern gland greasers so they came out as well. Once unbolted the gearbox just slide away and then we put it on the van! 5 mins?

Once the gearboxes were off then the flywheels were removed from both engines and the oil seals replaced. Then it was a question of just getting the new gear boxes and lining them up - rather a manual task as there was no crane - but once they slid onto the splines it took as long as it took to do the bolts up - 20 mins? Then the sfats were reattc hed to the gear boxes. This actually took a little longer as the bolts had to be "adapted|". Oh and some re-routing of the gear change cables as well. The original ones were too short.

I reckon that if the actually time taken was listed it was not more than myabe 6 hours in total. No pipes could got yesterday but we are hoping to get the boat back in the water tomorrow night. Having put in a new loo, moved the water pump and other bits into the lazarette and fitted a new bilge pump with re-routed plumbing. New anodes and antifouled with a few bits of gelcoat work - a total of 4 days. We also had to have a new prop washer made today, and that won't be ready until the morning (Tuesday).

Why did we change them? Motala gets a lot of use at slow speed, loads of coming alongside with a lot of in and out of gear. The existing boxes were/are working fine, but becuase of the cost we bought the boxes for it made sence to make the change. This was also made easier byy the fact that we had chnaged the engines 18 months ago and we were still running the old gearboxes and props that were not making full use of the engine rev limit.

At one point we thought that we were not going to make use of the boxes as the gear ratios were very different, but Lancing Marine and Storebro ame to our aid and after nearly a year we are ready to test.





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If the pitch of a prop can be changed to such a large degree why do they make so many different gear ratios ?

Are there any advantages/disadvantages to small gear ratio--------large prop pitch.




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They don't make that many different ratios. In fact with the gearboxes we have replaced with they made them in 1.96:1 and 2.68:1 only. It is the engine/s and hull shape that make prop selection such a black art and Burgundyben refered to it as. We didn't change the existing props at all - we had new ones made. The computer projection for the speed running at the engines' WOT of 3.9 has been given as 28 knots. We don't think we will achieve this but that's not our objective, after all Motala is semi displacment.

I hope that better engineers than me (not hard to be honest, I take the pictures me and spanners don't go well together) will explain the different gearbox ratios - that will enlighten me as well!!
 
I remember doing some research on props etc. a number of years back ... but in principle research seems to reveal that a larger prop, with less pitch ("ligheter loaded") is more efficient than the opposite...

Wrote some more about that a couple of years ago when discussing Surface drives .... now have to look into researching the subject again...

http://www.ybw.com/forums/showflat.php?C...&PHPSESSID=
 
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