As there seem to be a few Vertue Owners logging in I thought it might be useful to describe Sumara’s engine and the charging arrangement and to open up some thoughts as to the ideal horse power for a Vertue. I seem to remember coming across one Vertue with a 20 hp engine and I believe some have 10 hp Yanmars. I suppose the engine size depends on what you propose to use the yacht for. If you moor at the head of a strongly tidal estuary and you mainly sail at weekends then perhaps 20 hp would be a good choice. If you like to venture further afield, then a smaller engine will allow for a larger fuel tank. I like the 12 hp size, it has a bit of grunt when needed (especially with the alternator turned off – I’m coming to that!) and yet it will gently push the yacht through hundreds of miles of flat sea when the calms set in. A worry with a large engine is the tendency for Vertues to squat. When Terry built Sumara he was well aware of this problem and sneaked in an extra couple of inches to the turn of the bilge under the cockpit. Even with this extra buoyancy she sits down when all the crew are snugged up aft. My feeling is that a larger and heavier engine would result in needing to add weight up forward with a negative effect on her ability to respond to large waves. Going smaller would be fine but it could be a struggle to get into harbours like Dover against a spring tide (even with 12 hp, Dover needs care if the timing is wrong).
Sumara has a 12 hp Kubota which Terry maranised. Transmission is via a Hurth gearbox. She is solidly mounted to heavy bearers and raw water cooled. As the engine is now 22 years old with a good few hours I am able to vouch for the installation and the raw water cooling. Being solidly mounted allows for the engine controls to all be via stainless rods rather than cables. This makes the controls pretty bullet proof. The raw water cooling simplifies the engine and results in far better belt grip on the alternator because the belt does not have to drive the heat exchanger pump and therefore has a 180° grip on the alternator pulley.
When I installed the Eberspacher heater for the first Arctic trip I had to give consideration to the battery capacity. I spent a year or two researching and, with the help of Merlin Power, came up with the following highly successful solution.
I installed a Balmar 75 Ah marine grade alternator. It is twice the size generally used on this size of engine. I also installed a Balmar controller which enables me to run the alternator at half power or turn it off entirely. So now I have and engine which, at the flick of a switch, turns into a generator to charge the batteries at anchor. On full power it takes about 3.5 hp off the engine. The extra load put on the engine while charging at anchor helps to prevent the cylinders from glazing (so they tell me!). I can also turn the alternator off when I need every bit of motive power I can get to round the harbour wall.
To make use of all this power I changed the batteries to Adanced Glass Matt batteries choosing a 105 Ah (or was it 120 Ah) general service battery and a small light punchy 45 Ah engine start battery. I actually saved weight on the old twin 75 Ah lead acid batteries while dramatically increasing the capacity. Furthermore there is no chance of leakage of acid into the bilge. The batteries charge faster too so in no time the little engine has topped everything up.