Hull speed

[duluthboats]

Sadly Mike isn’t an active member anymore. Mike D passing
This thread is one his many contributions to this forum. We miss him.

Gary

[tspeer]

It almost doesn't. The resistance curves for a slender hull like an outrigger are much flatter than those shown.

Try http://www.cyberiad.net/michlet.htm instead.

[ErikG]

Well Gary since Mike D is no longer with us, he passed away some time ago he will not be able to respond to your post, but if you have any specific questions just ask and someone smarter than me will probably try to steer you in the right direction

ErikG

how can i make a hull go faster

[Willallison]

longer (displacement boats), lighter, more power....

ps. You're right - we do miss him - Dim as well...

[schecter]

Hello michael
Ive read ( some!) of your postings regarding hull speed. I have a 16 ton, 45 feet motorboat with two engines 375 hp each, that sits heavily in the water. Im planing to extentend the hull and the drive tunnels to gain lift at the back of the boat.topspeed full loaded is 20knots.
How much extension do i need? And will it help?

Pauli From Denmark

[sorenfdk]

Hej Pauli
Mike døde sidste år, så han kan desværre ikke hjælpe dig...
Men det er der heldigvis andre, der kan. Her i DK kan du f.eks. kontakte CDE Danish Marine Design, der har lavet den slags før. Se hjemmesiden på http://www.cde-dmd.com.
Og ja - jeg er involveret i CDE, så måske er dette ufin reklame. I så tilfælde undskylder jeg mange gange!

And for the rest of you:
I explained to Pauli that Mike sadly has passed away, but there are others who can help. In DK it could be CDE Danish Marine Design, with which I am involved. If this is unfair promotion, you have my excuses - it won't happen again!

[brian eiland]

I guess I was away from the list a little too long.....I missed the notice of Mike's passing as well. He was a great source of good info he shared freely.

I've wanted to bring up a subject that seems to be a trend amoung monohull folks lately. I can only think it has to do with the competition they are feeling from the multihull market. I continue to see these inflated claims as to their particular designs performance capabilities, particularly under sail.

Case in point. Have a look at the new PowerSailer from NZ.

Can you really believe that a 28 tonne (I would venture to guess heavier by the time its finished) monohull vessel will 'sail' at 18knts??...even with a 110' mast. The vessel is only 66' long and carries a 21' beam. And I imagine it will be very difficult to keep that underwater, retractable Z-drive housing/sea chest volumn free of sea water (lots more weight). And she's carrying around a 13.6 keel and twin rudders. Granted the small print says in a downwind surfing condition, but they advertise the vessel as though a perspective client should expect such performance....wishful thinking.

I've seen some number of other monohull manufactures claiming some 'very optimistic' speeds for their sailing performance lately....can't recall the specifics at the moment, maybe someone else can fill in the blanks.

Now to get to 'planing speeds' desired of this power sailer she's going to need 800hp....boy, that's not going to be light. Then how do you get the rt-angle gears of a Z-pod unit to stand up to a continuous hp rating of this magnitude??

Plus they're going to have a retractable keel (more weight) to gain entrance into shallow areas. And the vessel is going to be unsinkable??

It seems to me they should just accept the multihull motorsailer planform in the first place, as all of these goals (and there others) are met with this planform.

Boy I wish I could find a boater such as this gentleman, who would wish to put the money and effort he has committed into a custom catamaran motorsailer design. We could do this sort of performance with a 75' mast, two 200hp engines, and a 3.5' draft.....probably cheaper too.

[Corpus Skipper]

The TBD then got bigger, guns were added and voila – the Destroyer. The typical modern destroyer is around 400 feet long with a top speed of about 34 or 35 knots. Probably the propulsion system is CODOG meaning Combined Diesel Or Gas Turbine.

I'm an ex-Navy destroyerman. I was on USS Stout (DDG-55), one of the new Arleigh Burke class (DDG-53). She is powered by 4 GE LM 2500 gas turbines at 36,000 HP each, through double reduction gears (about 25:1 if I remember right) to J blade CRP props, counter rotating. 100,000 SHP after geartrain losses. Shaft torque was limited to 1.2 million (I think) lb/ft. Top speed was about 34 kt., burning a modest 20,000 GPH. I believe displacement was around 8000 tons. She is 505 ft. long, with a 60 ft beam (sorry, don't know the waterline particulars). Most of the time, we chugged along at 7-8 kt on 1 engine, dragging the other shaft. Much better fuel economy, something like 800 GPH.

[Corpus Skipper]

Oops, didn't read far enough ahead to see that my previous reply won't be read by it's intended recipient. He will be missed.

[PCVdominica]

Hey guys,
My 43' Gran Mariner currently runs twin 120 hp Perkins. She cruises at 8 with a max of 11kts. I am looking into a re-power and want to understand the characteristics of my hull before I choose new power-plants.
I have been reading and reading and I am still uncertain whether I have a displacement or a semi-displacement hull.
Would any of you hull-gurus mind taking a look at my pic and offering your assessment?
**Important to note: As you can see in the second picture, the props sit in hull recessions. I have heard this referred to as a tunnel drive system. Does that effect performance?

Kind Regards,
Marcus

[Corpus Skipper]

Marcus, that is a planing hull. V bottom at the stern, and submerged transom. Your speeds are only due to being way underpowered... If you want to keep similar performance, treat it as a semi-displacement. The tunnels do effect performance, via increased drag. But they do allow for a shallower draft, so it's a trade off. Nice boat, by the way. I'd call it "home sweet home"!

[PCVdominica]

Wow, a planning hull! In that case I imagine I am missing out on a great deal of performance potential. In addition, I am not maximizing the efficiency of my hull when I am tooling around at 10kts. I've been forming calculations for various power options on this site: http://www.psychosnail.com/BoatSpeedCalculator.aspx

I tend to like the equation that concluded i need 500 shaft hp to reach 30kts. I can find that kind of power in 6cly gas engines. Saving me some money.

Comments/concers?

Here us link to my photobuckt account, you can see many more pics if my 'Ever August' http://s35.photobucket.com/albums/d1...DSCN0182.jpgpg

[duluthboats]

Thanks PCV for bringing this thread to the top. It is a good example of the vast amount of information this forum holds.

PS, Craig, Good to see you are still out there. ;-)

[Perm Stress]

Tunnels allow for less inclined prop shafts; this make thrust, essentially orientated along the shaft, to push-forward more, and lift-up less, thus increasing efficiency.
Les oblique flow trough the propeller also increase efficiency and reduce vibration.
Propeller tip losses for part of the disc may also be smaller, but I am not so sure about this last point...
____________________________

As to speed, extremely important is weight, namely OVERweight. Ballpark figure I know from statistic analysis (certainly there are experts with more exact suggestions/numbers) is minimum installed power ~10-13kW/t to reach planing speeds.