GEARBOXES

[Micky]

Chris, i don't mind doing the 8knts at 2200rpm= nice speed, but not 4.5 at 1500rpm which the seller of the boat claims is all he ever cruised at and i wondered why.

The boat got up to the 8knts+ at 2200rpm ok, but the seller quickly closed down to 1500rpm again, this left a ? in my head why, and i asked myself how long would the engines last at a continouse 2200rpm. The boat is a "V" hull. By the way 2200rpm was not flat out on the throttles, i think it will go up to 2500rpm+

All this is new to me so please excuse my ignorance.

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[Chris_d]

4.5knts @ 1500rpm sounds typical and corresponds to normal river speed limit, if the boat has spent most of its life on the river it will have done 100's of hours at this speed. Probably to the owner though, 8knts and 2200rpm will have felt and sounded like warp speed and the engines were being thrashed, but actualy still very reasonable rpm. However these engines are very old and a Maderia 27 is only really a sheltered water craft, perhaps its not the best bet if you contemplating coastal use.

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[duncan]

those figures really sound fine - you will find yourself in areas that require you to be down at that speed (or lower) and you don't want to be having to kick in and out of gear.
At displacement speeds you are going to get a linear fuel consumption between 4 and around 7.5 knots for that hull and the engine isn't working much at 2200rpm anyway with those props gearing so leave it all alone! IN fact if you do change it the engines probably won't produce enough power to give you that extra knot currently available if you open her right up!!!

<hr width=100% size=1>madesco madidum ..../forums/images/icons/smile.gif

 

[Micky]

OK chaps, advice taken, leave alone. Thanks everyone.

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[SP2]

Re: Only 73?

Tend to agree your phylosophy. Not much around at about 10 metres that we would prefer to Spectrum Too (well except a Ranger 36) so even if we need new engines at some time that would be a cheaper/best option.

We stay in for the winter - how about you?

Mike

<hr width=100% size=1>That's Haswell - not hassle - www.spectrumtoo.org.uk

 

[miket]

Don't confuse "V" shaped hull with deep V planing hull.
They used to be called "Hard Chine" hulls, which whilst fairly V shaped were still full displacement hulls.
Another contributor has said there was a fast version, but to my memory it had a different shaped back 1/3 to the hull.

As you have been advised leave it alone and buy something else if you want to go fast.
Incidentally, he may have been hiding an overheating problem by not leaving it at full chat for very long. I don't recommend cruising at full revs but the boat should achieve the design rpm for the engines for short periods and cruise around 200 rpm down from max'. Having said that probably not much point if only gaining 1 knot. I would have thought that boat should cruise at 7 knots well within the engines max rpm.

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