Building our boat

Amazing thread!

If it's making a lot of noise and the engine rpm is increasing I'd suggest it were underpropped. Tabs should help - have you determined where the centre of buoyancy is compared to the centre of gravity? Do you know how much she displaces and what the boat now weighs?
 
The prop is indeed a 4 blader, 21x25".
When choosing the prop I got different proposals from different companys, from 3 bladers to 5 bladers, from 20 to 26 inch outer diameter. Seems to be no exact science.

Weight of the boat is +/- 11 tons, including full tanks. I don't know centre of buoyancy nor centre of gravity.
Maybe I have not enough power?
 
Are you still with the initially proposed engine, a single 160hp Weichai-Deutz 6-cylinder? If so I'd have expected that to be a reasonable speed given the hp rating.
 
My boat is semi displacement only weighs 7.5 tons maybe fully loaded 8.5. It has tabs and a five bladed prop and can do twenty knots but it takes 425hp (and my engine has loads of torque).
 
I hope to be corrected but I think you will need a lot more hp to lift your boat over it's bow wave and onto the plane and tabs or props are unlikely to give you much if any improvement in speed.
 
From someone who thinks cutting his toenails is a major engineering exercise .... you are an absolute hero! ... Congratulations on a fine looking boat.
11 tons and 150hp, I'd say 17kms would be about right ... you could try a different prop and trim tabs as suggested ... I'd try to find a prop expert if you can!
 
I didn't realise the engine was only 150hp.

My Yanmar 4LH-STE produces 230hp and on a boat weighing less than half yours with a semi-displacement hull reaches 23 knots @ 3300rpm WoT. I would expect you to need two of these engines to get anywhere near that.
 
Hello K, good to hear that the boat is in the water, must feel as a big acheevement/ relief, well done! I believe the speed you achieve is ok for the HP, you're slightly above hull speed, so you will need MUCH more Hp, for a significant increase of speed.
What about the battery charger? What is the problem? Can I help with something?
 
Hi,

The combi charges fine, but the batterys do not charge with the engine's alternator.
Tomorrow I will do some measurements to see if the alternator works ok, or maybe I have connected something wrong with the Cyrix.
I have only 1 battery monitor on the domestic bank, so maybe the starter batteries do load. Still have to find out..
 
The alternator is ok, but when the engine is on only the starter battery loads. Even after a 7 hour run of the engine the domestic bank does not load.
Makes it a difference if I switch the connections on the Cyrix?
 
kristof_dani said:
The alternator is ok, but when the engine is on only the starter battery loads. Even after a 7 hour run of the engine the domestic bank does not load.
Makes it a difference if I switch the connections on the Cyrix?
Click to expand...

no, normally this doesn't matter,
the cyrix links the two battery's, when the voltage on one side is above approx 13V, (see manual)
it does not engage when the voltage on one side is too low, < 12V, (sort of a safety feature when the domestic banc is too low)
you could add a puch 'link' switch, to "engage " the cyrix a few seconds,
and if the voltage doesn't drop too much the cyrix should stay "on"
there is a terminal on the cyrinx for such a switch.

you could also use a "starter" / jumper cable over the terminals of the cyrix, thats what I had to do on a few occasions on my Karnic.

with a voltmeter you can measure what's going on
 
The issue with the Cyrix is solved. Did forget to connect the little black wire to the domestic bank. Thought the little wires were only for emergency start... Stupid me.

Hereby some pics of the load of the boat.









 
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