There's a bug in the Matrix

[martynwhiteley]

There\'s a bug in the Matrix

Houston we have a problem....... I've found a way to defy the laws of physics!!

After the mad afternoon on the forum, there was only one thing for it. Get to the boat and commission my trim tabs.

I did so, and took it for a test, now consider the following:-

Boat before conversion......

3 1/2 ton of Birchwood 27 (hull length), not known for being speedie, big keel.

TWIN 120 hp BMW 2.0l petrols, with low tanks and crew, best speed = 24 knots.

(Note all speeds quoted are non-tidal, not wind assisted, gps readings)

Boat after replacement with SINGLE 1.7 litre 4 cyl diesel engine (prop rated at 116 bhp)..............

With FULL fuel and 3/4 water tanks, (but ok only me on board) - 22 knots !!!!!!

It rev's to the full 4400 rpm, so may even be a little 'under-prop'd !

I was 'blown away' by my first trial at 16 knots, but with the trim tabs down, and a little more 'running in'.............

Someone explain to me how this can be. MBM tests of the boat new with single 120 hp BMW petrol did 9 knots!!!!!!!! Even with twin 145 hp Volvo's it only did a (so called very respectable, but over the hull capability) 29 knots.

Those bu**ers at MerCruiser are trying to pass off a 250hp racing spec engine as a domestic 120hp obviously.

Perhaps it'll shake itself to bits after 150 hrs ?????????????

<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>

 

[MedDreamer]

Re: There\'s a bug in the Matrix

Were you going downhill?

<hr width=100% size=1>Martyn

 

[martynwhiteley]

Re: There\'s a bug in the Matrix

Well I was going pretty much due south at the time, but .................

None of it makes any sense, and they try telling you that a 33 foota with TWIN 150hp diesels is mega underpowered!!!

Still can't believe it /forums/images/icons/smile.gif .



<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>

 

[BarryH]

Re: There\'s a bug in the Matrix

What were you using to measure your speed, gps/log? I've found that the two gps's on my boat will read two different speeds at the same time. Only on a couple of occasions have I had them agreeing. They measure speed over ground and take no account of any tide running. So add or subtract any tide element.

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[martynwhiteley]

Re: There\'s a bug in the Matrix

Sorry Barry but....

The run was on non-tidal waters, no current, little breeze.

I only have one gps, but I do have a 'paddle wheel' Stowe log, and that was reading 21.6 knots, (the gps actualy max'd at 21.8 knots).

The boat was moving, no question, and don't forget I saw a full 4400 rpm on the tacho!

The bennets were fully down (and that helped to lift the stern, as my previous trial without the tabs plumbed in, was very 'bow-up'). The leg was fully down, raising it only a little seemed to cause cavitation. Mind you I did set the X dimension 20mm high, 'cos I didn't want to cut too much off the internal keel ribs to allow the engine to sit as low as it should have.


<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>

 

[BarryH]

Re: There\'s a bug in the Matrix

Couple of trains of thought then. Only one engine, so less weight in the stern. Only one sterndrive, so less drag. The new engine is putting out nearer the stated HP. The old engines were worn and not putting out as much power as you thought.

I would have thought the weight would have been the biggest factor in as much that the hull rides at a much more economical attitude to the water. Plus the fact that theres less drag from the single drive. And a drive that is a bit more hydrodynamic that the old 'boxy' beemer drives too boot.

Asfar as the rpm goes, this is a new engine, should you be running it balls out so soon!.......just a thought.

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[pheran]

Re: There\'s a bug in the Matrix

Sorry to be a kill-joy, but you know the old adage <font color=blue>'if it seems to be too good to be true, then it probably is'</font color=blue> Suggest you check all the variables again. seems highly unlikely!!

<hr width=100% size=1><font color=blue>A hangover is just the Wrath of Grapes</font color=blue>

 

[victor_meldrew]

Re: There\'s a bug in the Matrix

I'm with you pheran. 116 out of diesel = 240 out of petrol? Nah! Put simply I don't believe it. Either that or the marine engine world is about to be stood on its head If thsi can be shown to be true, I'm going to make a fortune out of buying up petrol engined boats and stuffing a tiddly oil-burner in them!!!!

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[ccscott49]

Re: There\'s a bug in the Matrix

I think you will find it's weight and water resistance, or lack of it, which is helping, plus better trim and the old engines were probably well on there way out and only producing about 80 each. If it felt fast, it probably was!

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[ccscott49]

Re: There\'s a bug in the Matrix

I think you will find it's weight and water resistance, or lack of it, which is helping, plus better trim and the old engines were probably well on there way out and only producing about 80 each. If it felt fast, it probably was! Rejoice and go have a pint or two!

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[tr7v8]

Re: There\'s a bug in the Matrix

Yes I know it'll wind up the sceptics but....
Old petrols and diesels were notoriously over spec'd and some blindingly optomistic HP figures claimed 'cos they didn't have the same standards as the car manufacturers to comply with.
The Merc has very high torque figures even for a turbo diesel which will help it.
Finally remember Spannermans post last year about reengining a Draco Twin Cab 2500 with a pair of Merc 1.7s. He reckoned it would blow off all it's equivalent twin 4 pot boats on the water. I think he quoted 38 knots, well spec seems to be 26-28 with Volvo 145As which are 138HP according to Volvo.

<hr width=100% size=1>Jim

Draco 2500

 

[Dave_Snelson]

Re: There\'s a bug in the Matrix

Twin engine down to single engine - less weight aft.

I believe these motors are the Isuzu 1.7L turbo D engines as fitted to Vauxhall Cavalier & Vectra. I used to have a Cavalier 1.7D back in 1993. On a motorway, I racked that car up to 121mph - without too much effort!

When the turbo starts to whistle, she just winds up and keeps on going. Pretty bomb proof too!

<hr width=100% size=1>Madoc Yacht Club
<A target="_blank" HREF=http://www.madocyachtclub.co.uk>http://www.madocyachtclub.co.uk</A>

 

[martynwhiteley]

Re: There\'s a bug in the Matrix

Welcome back Jim, been away?

Yes I suspect the old BM's were not giving out the rated power by a fair margin, and I agree that the BM drives look far more chunky than the new streamlined alpha. But where's Spannerman? Even he didn't think it would plane with only a single installation!

<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>

 

[duncan]

Re: There\'s a bug in the Matrix

it would appear that you have a very well matched package and should just get on with enjoying it.

With regards to buying up boats in the 23 - 28ft range and sticking both this package, the 4 cyl Volvo and the 240 Yanmar in them - I think you will find that this is increasingly being done; and the manufactures / importers are fiting them to new boats too!

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