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Message board > Engines > Slow noisy twin cylinder diesel engine

Message 9 of 9
Posted by member Calum Norris on Saturday 10 October 2020

Hi there, it looks to me like your Hull is a Hardy 20 M/S I.e. motor sailor. If this is the case then the speed will be limited by the hull shape and bilge keels that are obvious on the original photo. While I have sailed yachts at 8 ish plus knots, or more if it is a sports hull, that is probably about max. You therefore have to decide if pushing the hull at 10 knots, no doubt burning more fuel with a bigger engine is really worth it. I have recently bought a Hardy family pilot with a 60hp which is used in Scottish coastal waters and we locally have a tide race that runs at about 8 knots. I went through the other day and she stayed on the plane but probably as the tide slowed, certainly in the last third. I would not expect that at full flood. If you fit a larger engine it will spend most of itís life at low revs which is not good for any engine and the only reason to fit a larger engine would be in pushing a tide. Otherwise stick to a smaller engine with better economy and better suited to the hull. I wait to be corrected by those that know better.

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Message 8 of 9
Posted by member lynall on Sunday 4 October 2020

* Lazarette

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Message 7 of 9
Posted by member lynall on Sunday 4 October 2020

* Pic

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Message 6 of 9
Posted by member lynall on Sunday 4 October 2020

* Any direct injction diesel is going to be noisy, indirect might be the way to go.
We have volvo penta md22l in our 27, two direct injection engines and the noise was unreal at all rpms.
Loads more sound insulation everywhere incl all flat panels/hull/lockers/storage boxes, and all air gaps sealed with neoprene foam has made a huge diffference.
What I read and learnt (hopefully!) was you do not need to cover every surface in the engine bay/room. but enough to stop the sound bouncing
She plods along at 1800rpm doing 5 to 7 knots tide dependent, flat out 2500rpm and she once hit 9.5 knots and was very noisy!
We have accepted she is a plodder and live with it, speed is nice, but speed costs a lot in fuel.

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Message 5 of 9
Posted by member David Smith on Sunday 4 October 2020

Ok ten Knott's not going to happen.
But I do want to swap the engine for a quieter 4 cylinder diesel. Just checked the dimensions of the boat 🙄 not a not of space. I would appreciate if anyone knows of an engine to suit.

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Message 4 of 9
Posted by member Graham Clay on Sunday 4 October 2020

To get to 10kts+ you will need to get her planing. From previous discussions on this board, that takes about a 50hp outboard. Trim tabs also help. Not seen anyone try with an inboard diesel, but given enough power...
You will also probably need a different prop to match a higher engine power - again, see other discussion threads.

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Message 3 of 9
Posted by member lynall on Saturday 3 October 2020

If you google hull speed calculator, or prop speed calculator, so long as you have access to your hull and prop for measurements, you should be able to work out what it can do speed wise.
In a nutshell to exceed a semi or full discplacement hull speed takes a lot of power and fuel.

Some examples, many more out there,

https://www.easycalculation.com/physics/classical-physics/hull-speed-calculator.php

https://www.vicprop.com/displacement_size.php

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Message 2 of 9
Posted by member David Smith on Friday 2 October 2020

* I am looking at an engine upgrade. Is 10 knots possible with correct engine and prop???

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Message 1 of 9
Posted by member David Smith on Friday 2 October 2020

* Hello everyone I am new to the club.
I would like to change my twin cylinder diesel engine for a four cylinder.
Any ideas

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