Speed log impeller - keep or remove

[BoatingBeginner]

I've got an old VDO Sumlog on my semi-displacment mobo. In the age of GPS it is an irrelevance, isn't it? Okay, GPS can fail, but I don't need accurate speed measurements for navigation as I use the GPS and radar and I'm rarely out of sight of land. Also, what's the point of knowing speed through the water when GPS will give me speed over the seabed.

The impeller must slow the boat down and I need all the help I can get to make a sensible speed.

Should I just cut it off and fill the (GRP) holes up?

What would you do, folks?

 

[sarabande]

Are you a believer in the Worst Case ?

 

[BoatingBeginner]

Which worst case - that all the world's GPS systems are going to fail or be switched off? No!

Or that a through-hull fitting seal might fail?

 

[john_morris_uk]

You will find some people who say keep it and some people who say fill the hole and do without.

I am on the side of believing that a log that says how fast I am going through the water and particularly how far I have travelled is essential for navigation when other means fail.

The log impeller does not slow you down - not in the way that a fixed propellor does with its drag. If you don't keep the log impeller at least get a towed log so you can navigate when the GPS dies.

I am not sure that saying you are within sight of land is an excuse for anything. Which bit of land is always the problem...

 

[john_morris_uk]

Which worst case - that all the world's GPS systems are going to fail or be switched off? No!

Or that a through-hull fitting seal might fail?

They might not be switched off, but I have had my GPS antenna cable fail - no fix - nada - nothing.

Just like I can't think of a year in the last twenty five when I have been on a yacht sometime and found that the engine wouldn't start. Never happens does it?

Anyway, the difference between speed through the water and speed over ground gives you the tidal stream. Always a good thing to check on and make sure you are doing the right thing.

 

[prv]

Just like I can't think of a year in the last twenty five when I have been on a yacht sometime and found that the engine wouldn't start. Never happens does it?

I have. Unfortunately an overenthusiastic crew member had just released the mooring (one of the visitors' buoys at Beaulieu) without being asked, and we drifted down on quite a fast ebb right on top of a gleaming varnished gentleman's motor-cruiser.

Fortunately no damage done, and the guy who was on the helm can do a Posh Yottie manner with the best of them, which mollified the chap in the badge-encrusted blazer.

Anyway, the difference between speed through the water and speed over ground gives you the tidal stream. Always a good thing to check on and make sure you are doing the right thing.

Clearly so on a sailing boat - it amazes me to hear of sailors removing logs as some do. But is it quite so important to the mobo fraternity? A knot or two of tide hardly matters when you can do twenty.

Pete

 

[BoatingBeginner]

But is it quite so important to the mobo fraternity? A knot or two of tide hardly matters when you can do twenty.

This is what I'm thinking... and it seems to get weed snagged to it quite a bit, too.

 

[William_H]

Log paddle

I removed my log paddle and glassed over the hole about 12 years ago. No regrets. The paddle was more often than not encrusted with growth such that it would not turn.
The Sumlog is a more robust type of screw propeller and perhaps not so subject to growth (especially in UK) However you can't withdraw it and clean it. So i suggest leave it there and use until such time as you find if fouling is a problem. olewill

 

[BoatingBeginner]

The Sumlog is a more robust type of screw propeller and perhaps not so subject to growth (especially in UK) However you can't withdraw it and clean it. So i suggest leave it there and use until such time as you find if fouling is a problem. olewill

It's encrusted with barnacles right now - part of my thinking behind getting rid!

 

[john_morris_uk]

It's encrusted with barnacles right now - part of my thinking behind getting rid!

But in another thread you admit the boat has been lying afloat for three years...

 

[BoatingBeginner]

But in another thread you admit the boat has been lying afloat for three years...

Guilty, m'lud!

The boat had engine problems and was being used in Spain as a liveaboard. It didn't move much in that time, but if I realised how solid all that growth was I'd have taken her out of the water and scrubbed her sooner.

Now she's back in the UK, not being lived on, and I want to be going places in her - at the speed she was intended for!

 

[rivonia]

Only you can make the final decision. Heres my two pennies worth. KEEP it. Put the block in and leave it nice and clean inside. When all else fails stick it back in. A log is what it says it a LOG it does other things as well as speed. On the ships log you will need to enter distance as well as speed, makes sense to me but as stated you will make the final decision irrespective of the forums oppinions.
Good luck

Peter

 

[BoatingBeginner]

Only you can make the final decision. Heres my two pennies worth. KEEP it. Put the block in and leave it nice and clean inside. When all else fails stick it back in. A log is what it says it a LOG it does other things as well as speed. On the ships log you will need to enter distance as well as speed, makes sense to me but as stated you will make the final decision irrespective of the forums oppinions.
Good luck

Peter

Thanks for your input.

Which block? It'd be a good compromise if I could just take the impellor out and leave the 'fin' in case a future owner wanted to rig it up again...

 

[john_morris_uk]

Thanks for your input.

Which block? It'd be a good compromise if I could just take the impellor out and leave the 'fin' in case a future owner wanted to rig it up again...

Most through hull impeller logs are built to be able to be withdrawn into the boat so that they can be cleaned. Lots of people get into a tiz over the water that comes in when they are withdrawn, but most impeller logs also have a blanking 'dummy' fitting that you can put into the tube to seal it off while you fiddle around cleaning the log impeller.

I think the suggestion was that you fit the blanking one in place, and leave it at that. If you haven't go the blanking bit, then I am sure that you can pick one up somewhere. What make log is it?

 

[Skysail]

GPS aerials fail too. I once crossed the channel in fog, making a good landfall with GPS. The following day - no GPS!

 

[William_H]

Most through hull impeller logs are built to be able to be withdrawn into the boat so that they can be cleaned. Lots of people get into a tiz over the water that comes in when they are withdrawn, but most impeller logs also have a blanking 'dummy' fitting that you can put into the tube to seal it off while you fiddle around cleaning the log impeller.

I think the suggestion was that you fit the blanking one in place, and leave it at that. If you haven't go the blanking bit, then I am sure that you can pick one up somewhere. What make log is it?

Yes but this is an old Sumlog with a bowden cable drive to a mechanical speed and log. As I remember the spinning part a long screw like a propeller is attached and the cable pushes into it from the inside. I bought one about 40 years ago. It may however be a later model with the same kind of impeller but electrical impulses to the head. Either way I think you remove the whole thing. A hole about 15mm in diameter and 4 screw holes so easy to f/g over. Or I may be wrong of course. But as said I think it worth cleaning it. make it work and see how long it keeps working. If it fouls up quickly then remove it next slipping. olewill