Subdued start to the new season

May 11, 2013

Macwester Malin 32 on mooring

We’ve had a pretty subdued start to the season. The weather hasn’t been great in Scotland and yet we’ve watched, listened to, and read forecasts of hot sunny days further south in the UK. The fact that winter hasn’t fully retreated yet, arguably makes our ‘current‘ technical problem slightly easier to swallow. During one of the half-decent weekends that we had recently, we intended to head out for our shake-down sail. Unfortunately just before we were about to set-off our plans were scuppered when our Malin’s engine wouldn’t start.

heavy duty battery isolator switch

Our Macwester’s Lombardini diesel engine is a reasonably recent replacement engine with low hours so we reasoned that a problem with the starter motor was unlikely. After a few simple diagnostics we were reasonably sure that the batteries were flat, so we took them home and I gave them a good charge. Both batteries appeared to maintain a healthy charge over several days. I was a tad confused as to why there should be a problem with either of the batteries, and given that I had nagging concerns about the Osculati main isolator switch (above, left switch), I bought an identical replacement and swapped these over. With the timely help of a passing friend, we managed to get the batteries back on board our yacht. I should perhaps mention that as the batteries are both half a metre long, I can’t tell you how happy I was to bump into the passing friend I mentioned, as I really hadn’t worked out how we were going to get the batteries from a bobbing dinghy back on to our Macwester Malin. Before long I had both fully charged batteries reconnected.

Trip to Capernaum

Unfortunately the engine still wouldn’t start. By this stage, we knew for sure that this was a battery problem as we had started the engine in the interim period with a car battery. Deciding to try to start the engine with one single battery, I persevered and after trying three combinations of the 2 x leads to 2 x battery terminals I got the engine started on the fourth and last combination. We decided to head to Capernaum where we would get easy pontoon access to fix the problem …whatever it was.

Macwester Malin on pontoon

The short journey was completed without any problems, although the wind was gaining in strength and we were taken sideways as we entered the harbour. Of course we couldn’t rely on the bow thruster because of the battery problem, nonetheless we managed to get on to the pontoon easily given that there were friends ashore to take the ropes.

On Sunday the 5th of May the wind changed direction and with the tide well in, by midnight we were getting a bit of a bashing from a south-easterly (from the direction of 11 o’clock in the photo above), which was bring waves right into the harbour and pushing us against the pontoon. I got up and sat on watch for half an hour. Our Malin’s bow and stern were swinging up and down by anything up to 0.75 of a metre at times, but the centre of the yacht was relatively still and I reasoned that there was no danger that our new navy blue Majoni fenders were going to ride up over the pontoon as they’re 0.7m tall. Eventually I went back down into the aft cabin and managed to nod off despite the fairground ride and sound of the waves slapping firmly into our Mac’s hull.

Holt 450 stanchion block

The following day, while I was scratching my head and taking advice on the battery problem, I took advantage of being on the pontoon to do some smaller jobs. This included swapping out an old stanchion block, which was a bit sticky when we were operating the head sail, with a new Holt 450 block. Hopefully we’ll notice the difference when we eventually get out for our shake-down sail. At the same time, ‘the crew’ re-did some whipping on our new fenders, as she wasn’t happy with the first attempt.

Yuasa Cargo battery

With the help of a friend from the club, we discovered that one of the batteries dropped from over 12v to about 4v under load. The old battery didn’t go without a fight; later we discovered that it had chewed through my jeans and my hoody as I wrestled it off to the recycling centre. Our friend kindly sourced a replacement Yuasa Cargo battery with 143 Ah the following day and he even managed to swing a better deal than the £190 retail price for us [yay!]. With that, our Macwester Malin was fully operational once more. However we still had a small problem of some sort, as there was a spark when the leads were connected up to the batteries even although the isolator switch was off. This meant that there was something constantly drawing power from the batteries.

I reasoned that this problem was likely to be something that had been happening since we bought our Macwester 32 early in 2011, and that we had been able to sail throughout two seasons despite it. Nonetheless I decided that it made sense to keep going and try to identify the problem, rather than just live with it and assuming that everything would be okay as it had been previously.

Macwester Maline bow thruster

This post is already overly-long so I’ll finish up now. As things stand, we’re fully operational. According to another friend (and electrician), it might be the bow thruster that is the source of the spark, or more accurately perhaps a sticky relay that sits between the batteries and the bow thruster. We’re still running diagnostic checks, however one solution might be to introduce a new standalone isolator switch for the bow thruster. We’ll keep going and we’ll find a solution over the coming week or two. The good news is that at this stage it looks as though there’s nothing that will stop us from going out for our shakedown sail come the next suitable day that we have free.



  1. Hi. On my Macwester, when the isolater is off the auto bilge pump and float switch is the only thing connected and that would only draw current if the float contactor switch is on i,e. water in the bilge at that point. Also the spark would be fairly small. Unless there is a short? If it’s a large splat it wont be that.
    Daft question but? Do you have two batteries in parallel on Bat1? and leisure batteries on bat2?. If so are the two main batteries in parallel, positive to positive and neg to neg ? Also the two batteries should ideally be the same Ah and both be traction batteries not leisure or mixed. Of course if you bought just one newly charged battery, at connection to the other one it would be trying to transfer charge to the other flatter one in trying to level up so current would pass between them until they both had equal charge thus giving a spark at connection.. Also worth having the second battery checked at an auto electricians properly to see that it is taking a large enough charge. Although a battery may show as fully charged after being on a mains battery charger and show well over 12 volts it could be aged and only have a small charge capacity. Presumably you have two traction batteries for starting on Bat1 and two leisure battieries on Bat2 for instruments etc? When I bought my macwester it came with two different Ah sized batteries on (Bat1), one leisure and one traction. Also the traction battery showed fully charged but not to proper Ah capacity. Changed them both out for new traction batts and problem solved. Dont start the engine on leisure batteries unless its a last resort. Yes it will start but bugger the battery in time.


  2. Hello Peter, Thanks for your thoughts. I’m still not sure what the problem is, but I’ve been narrowing down the possibilities. There are two batteries, both 0.5m long. They’re essentially truck batteries not leisure batteries. I didn’t know that the spark could be charged by the batteries equalising – so thanks for that.

    The new battery is 900 CCA / 143Ah. An engineer friend checked the older battery and it still maintains a healthy charge under load. The engine can start off either battery, but the protocol is to use battery 1 for auxilliaries such as the lights and nav equipment, and battery 2 (the new one) for the engine & bow thruster.

    My current plan is to isolate battery 2 in addition to battery 1. This will mean that no matter what is drawing power …nothing will be able to drain the batteries when we switch off the isolators. That seems like the most pragmatic ‘in-season’ solution.

    Thanks again and happy sailing!


  3. Hi, If you have the two batteries separated by the change over switch as Bat1 and Bat2 then they are totally separate (except perhaps for the common return) and the transfer thing should not happen. Assumed wrongly that you had two in parallel sorry.
    You will still have your autobilge connected wont you when the isolator is off? Is there also a security alarm system?
    If you connected the batteries when the isolator was still connected to that battery then anything could have been left on by mistake . On mine the gas detector is always on when a battery is connected at the isolator, hence the clicking sound at first switch on. The bow thruster presumably is via the isolator and not in cct when the isolater is off. Was the spark at connection with isolater on bat 1, bat2 or off? Bet your not sure now you are away from the boat? Good luck tell us how you get on.


    • Hi Pete,

      I’m far from an expert, but I think that although there are neutral cables connected across both batteries, the positives aren’t joined so the batteries are actually separate (absolutely no need to apologise). We don’t have an auto bilge at the moment (it’s on my list) but there are lots of auxiliaries hard wired directly to the batteries (including the bow thruster). We must have been pretty diligent at turning these items off at their individual switches, as before I started looking at this issue I had wrongly assumed that the master isolator would have shut the whole electrically system down. It does not.

      You’re right of course …I’ve been through so many diagnostics that I’m not sure what the on/off configuration of switches and batteries was when the spark happened. However I know that the sparks happened local to battery two and the additional positive cables added to battery two. The additional cables were 1) the bow thruster and 2) all other auxiliaries.

      My ‘in-season’ solution is to take “2) all other auxiliaries” from battery two on to battery one where there’s an isolator …and to fit an isolator to battery two. I’m trying a simple ZoomerRoo product that looks like an easy fit isolator (straight on to the battery) which has a claimed 400amp continuous rating and 900 amp intermittent rating. My thinking is that stopping the power at the batteries stops the risk of a drain, and I should be able to exclude auto-bilges, alarms etc from that isolator by connecting them straight to the battery; of course that will mean a wee bit of extra cabling to separate them from the other auxiliaries.

      I’ll include this info in a post at some stage.

      Thanks again for your help Pete!


  4. Hi from “Tara” Mac Malin – your replacement lombardini 30hp engine, from your excellent photos the prop looks original, do you know the prop dimension and pitch and if LH / RH as I think mine has been replaced at some time with the wrong prop. Many thanks your blog is a great read.


    • Hey Chris, Thanks for your kind words. I’m sorry, I don’t currently know the prop spec or whether it’s original. If you can be specific about the dimensions you require I can have a pop at getting those for you …unfortunately I can’t promise to have it done quickly, but if you’re not in a hurry let me know and I’ll see what I can do. Also would be delighted to include a few photos of Tara in the photo bank if you feel like sending them in.


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