Tod Tuna- what prop?
Tod Tuna- what prop?
I've read with interest past posts re. these early fast? boats. Having just nearly sorted one (codpiece) out enough to do the old 'Sea Trials' I'm sure it's wrongly 'propped' and I'd really appreciate contact with any other owners hopefully to compare notes etc. I've had suggestions/help from loads of people inc. a full calculation from the specialists re. the right propeller but even they questioned their findings so it's getting just a tad frustrating.... I've only just joined so as soon as I'm used to how things work I'll praps post some photos of the boat and perhaps might find a previous owner of my boat (used to be 'Tardis').Thanks all.
Re: Tod Tuna- what prop?
What prop diameter and pitch are you running at the moment? and what engine revs are you reaching? Compared with what you should be reaching.
Prop calculators nearly always over estimate the slip factor for these early hulls. Producing a prop with too much pitch.
Engine struggles to reach its full rpm and therefore doesn't reach full power.
Cheers,
S
Prop calculators nearly always over estimate the slip factor for these early hulls. Producing a prop with too much pitch.
Engine struggles to reach its full rpm and therefore doesn't reach full power.
Cheers,
S
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* Swinging the World by the tail since 1960 *
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* Swinging the World by the tail since 1960 *
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Re: Tod Tuna- what prop?
Thanks for your interest. Damaged 17x13 removed and replaced with 16x13. Perkins 75tdi s'posed to max at about 4500.Reaches 6ish Knots between 2 - 2500 then only another 1 + until 4-4500 rvs showing. Loads of conflicting suggestions about pitch. At the start I assumed it needed the 'bite' of a bigger prop and pitch so I'm now more confused than ever (which is quite some feat!) Before I pester anyone too much I need to get my hands on a shaft rev. counter to see if there's any slip at the gearbox end. (Newage 2:1) Not expecting the published 20+ Knots I've seen cos I think that might refer to the very early ply models but I would have thought 12 -14 was realistic. Thanks again Graham.
Re: Tod Tuna- what prop?
75Hp @ 4500 rpm with a 2:1 gearbox.
Displacement assumed 4000lb. (just shy of 1.8 tons all up)
IF the engine is producing 75HP
AND the gearbox isn't slipping:
THEN
PROP_SHOULD_EQUAL: 16" Dia by 10" pitch giving you about 20 knots. (All approx, depending on the weight)
If everything was connected OK, I'd expect the engine to struggle to reach max RPM. So the fact it is, then the gearbox clutch plates are probably U/S
So your plan to check the shaft RPM would be a good one.
Two by 50HP Watermotas used to get one of these to 22 knots according to the brochure - but I suspect it would have been heavier.
Cheers,
S
Displacement assumed 4000lb. (just shy of 1.8 tons all up)
IF the engine is producing 75HP
AND the gearbox isn't slipping:
THEN
PROP_SHOULD_EQUAL: 16" Dia by 10" pitch giving you about 20 knots. (All approx, depending on the weight)
If everything was connected OK, I'd expect the engine to struggle to reach max RPM. So the fact it is, then the gearbox clutch plates are probably U/S
So your plan to check the shaft RPM would be a good one.
Two by 50HP Watermotas used to get one of these to 22 knots according to the brochure - but I suspect it would have been heavier.
Cheers,
S
********************************************************************************
* Swinging the World by the tail since 1960 *
********************************************************************************
* Swinging the World by the tail since 1960 *
********************************************************************************
Re: Tod Tuna- what prop?
Thanks again, 16x10 was same calc. as Hamble props so that's re-assuring. Prob.test at weekend.Cheers