A 39' "downeast" influenced design - Feedback Request

[dobsong]

Originally Posted by Willallison

Mas -
Setting aside any issues of squatting and any subsequent inefficiency, the boat would require approx 136 SHP to run at her semi-displacement cruise speed of 14 knots (SL = 2.26). Again setting aside any losses occured thru the transmission etc, the Yanmar 6LP 315 hp engine should consume around 25 lph at that speed, giving a 25 hr (or 350 nm range) with a 10% reserve.

Hi,
Anticipating a little less consumption (say 20-22 lph) wanted 350 nm range as minimum @ 14 knots. Expecting that range will increase very significantly for a slow cruise (say around 8 knots). Trying to get all elements (prop, hull, engine etc) optimised for 14 knots. There are other similar boats that indicate all is achievable.

[dobsong]

Originally Posted by rwatson

Hi Dobsong

Thanks for the info, but I am an old tasmanian, and am very familiar with all the great timbers available. I have contact with a Celery Top Mill in the Huon Valley, but am always on the lookout for new sources.

The price is astronomical these days as is all timber.

If its not a secret, I would be interested in hearing about new sources and indicative prices.

Once again, I have little knowledge of Celery Top being used in epoxy work, as boats built with it rarely need any additional structural support until they are much much older.

Huon Pine was another major jewel of a Timber, but you would not be able to use Epoxy on it without a lot of treatment for the oils.

I suspect some sources of Celery Top could be a bit oilier than others, and may need to be treated accordingly berfore epoxying.

Were you going strip planking for the design ?

Yes the hull is to be strip planked (cove & cusp 23mm x 42mm) with exterior 450 gsm DB + 600 gsm DB and interior 2 X 450 gsm DB. I have not heard of any problems with glue or epoxy adhesion for Celery Top.

Celery Top logs available for milling on the west coast. Around $20,000 for the quantity (+15%) I need. Will use celery top for other parts (in addition to the hull) also using marine ply for a few places. Builder, designer and myself all agree we will end up with a very solid hull.

Apart from the expense and some problems with oils, my view is Huon is too soft. Also its very hard to get it in suitable lenghts for a 40' boat.

[dobsong]

Originally Posted by Willallison

Mas -
Setting aside any issues of squatting and any subsequent inefficiency, the boat would require approx 136 SHP to run at her semi-displacement cruise speed of 14 knots (SL = 2.26). Again setting aside any losses occured thru the transmission etc, the Yanmar 6LP 315 hp engine should consume around 25 lph at that speed, giving a 25 hr (or 350 nm range) with a 10% reserve.

With a displacement of 6,000 Kgs (now 6,100) and a conservative co-efficient applied the designer has calculated the following:

For the 315 hp max output using 85% (again a very conservative approach) of this figure (268hp) shows that the craft should do 21.7 mph or 18.9 knots.

To do 14 knots or 16.1 mph, same coefficent, the actual HP required is 125 hp.

[Willallison]

So, essentially the same as my quick estimate. The consumption I gave was based on Yanmar's own prop & power curves. If they are correct, I'll be surprised if you can get much better than that - it equates to 2.5 nmpg, which is pretty good going for a semi-displacement boat. Having said that, my own recent experience with a Yanmar 6BY260 showed that (in my instance at least) Yanmar's figures were quite conservative.
Just as an aside, I reckon you'll find the engine is happier running at around 2400 rpm - which should give you 100shp and around 12 knots, or thereabouts.
You will certainly see a BIG jump in your mileage if you slip back into displacement mode: 8 knots max

I'm a bit short on time at the minute, I'll take up the debate with you about tender access at another time...

[dobsong]

Originally Posted by Willallison

So, essentially the same as my quick estimate. The consumption I gave was based on Yanmar's own prop & power curves. If they are correct, I'll be surprised if you can get much better than that - it equates to 2.5 nmpg, which is pretty good going for a semi-displacement boat. Having said that, my own recent experience with a Yanmar 6BY260 showed that (in my instance at least) Yanmar's figures were quite conservative.
Just as an aside, I reckon you'll find the engine is happier running at around 2400 rpm - which should give you 100shp and around 12 knots, or thereabouts.
You will certainly see a BIG jump in your mileage if you slip back into displacement mode: 8 knots max

I'm a bit short on time at the minute, I'll take up the debate with you about tender access at another time...

Advice from the designer is that conservatively I will need 125 hp at the prop to achieve 14 knots. From the propeller curve we see that this is delivered at around 3,000 rpm. From the fuel consumption graph we see that the engine uses 30 litres per hour at full load at 3,000.

It is a bit of a “SWAG” (scientific wild arsed guess) but given we are using less than half the available horse power at 3,000 rpm (or half allowing for losses) I am hopeful 20 litres per hour is achievable. This seems to be supported by outcomes achieved by similar boats.

What do you think?

Regards, Graeme

[rwatson]

Originally Posted by dobsong

Yes the hull is to be strip planked (cove & cusp 23mm x 42mm) with exterior 450 gsm DB + 600 gsm DB and interior 2 X 450 gsm DB. I have not heard of any problems with glue or epoxy adhesion for Celery Top.

Celery Top logs available for milling on the west coast. Around $20,000 for the quantity (+15%) I need.

Thanks for that info. If you get the chance anytime, I would be interested in the cost per cubic metre. I costed Plantation Kiri recently - its over $4000 per cubic metre.

[Willallison]

Propeller curves can only ever be regarded as an estimate IMHO. There is simply too much variation from boat to boat and installation to installation for it to be regarded as anything more than that. The only definitive consumption figures come when the boat hits the drink. They should, however, give a reasonable approximation and anyone with a bit of common sense would make allowances for any variation from theoretical to real life. Your designer has suggested that you'd need 700 L to run 350 nm at 14 knots and my quick estimate would suggest that that's pretty much on the money, allowing a 10% (70L) reserve. That is (as Mas pointed out) assuming calm conditions.
My quick look at the 6LP's prop curve earlier (I assume it is the LP that you're planning to use...?) suggests that 27-2800 rpm ought to yield aound 130 hp at the crankshaft. This is under load - that's what the prop curve is intended to estimate. At 2800 rpm the engine will use around 25 lph, according to Yanmar's figures. Based on that, 20 lph may be a bit hopeful... but as I said, my recent experience with the 6BY yielded substantially better fuel consumption than the published Yanmar figures. Personally, I would expect the worst and (hopefully!) be pleasantly surprised when the boat performs better than expected.

[dobsong]

Originally Posted by Willallison

Propeller curves can only ever be regarded as an estimate IMHO. There is simply too much variation from boat to boat and installation to installation for it to be regarded as anything more than that. The only definitive consumption figures come when the boat hits the drink. They should, however, give a reasonable approximation and anyone with a bit of common sense would make allowances for any variation from theoretical to real life. Your designer has suggested that you'd need 700 L to run 350 nm at 14 knots and my quick estimate would suggest that that's pretty much on the money, allowing a 10% (70L) reserve. That is (as Mas pointed out) assuming calm conditions.
My quick look at the 6LP's prop curve earlier (I assume it is the LP that you're planning to use...?) suggests that 27-2800 rpm ought to yield aound 130 hp at the crankshaft. This is under load - that's what the prop curve is intended to estimate. At 2800 rpm the engine will use around 25 lph, according to Yanmar's figures. Based on that, 20 lph may be a bit hopeful... but as I said, my recent experience with the 6BY yielded substantially better fuel consumption than the published Yanmar figures. Personally, I would expect the worst and (hopefully!) be pleasantly surprised when the boat performs better than expected.

Yes – conservative/realistic 25 lph @ 14 knots x .9 = 352 nm but hey I’m a hopeful sort of guy and my optimistic “hope” is 20 lph @14 knots x .9 = 441… sweet!

Also the displacement calcs are "realistic" with full tanks and cruising gear included.

The graphs I forgot on my last attached

Some information that supports my fuel consumption "guesstimates"
- The Rumery 38 with the 315 hp Yanmar is reported in the Wooden Boat article as having a top speed of 32 mph and using 6 gallons (23 litres) per hour at 30 mph. A surprising figure! I’m guessing what was actually meant was that it averaged 6 gallons an hour for 100 hours operation at speeds of up to 30 knots, still OK in my book.
- Given the boat being designed for me has more beam, bigger tanks and a bit more in the cabin fit out (an extra 1,100Kg displacement fully loaded above the 5,000Kg reported for the Rumery – was it 5,000??) I’m assuming we will loose around 10 knots top end speed and have some increase the fuel consumption.
- The 32’ Cheviot (32’ x 10’ 10” x 3) built by Tim Phillips is shown in her trip across Bass Strait as having a top speed of 24 knots and that with a 300 hp Yanmar at 3,000 rpm she travels at 15 knots using 22 litres of fuel per hour.
- The Fairway 36, a semi-displacement hull that displaces 7 tonnes fully loaded, has a top speed of 19 knots when fitted with a single Yanmar 6LP-STP. With this engine at a cruise speed of 15 knots the fuel consumption is reported to be 19 litres per hour.

But at the end of the day these are interesting "facts" that I use to give me some comfort (along with calculations from the designer) - the real test will be when she is launched and I do a decent run in her with some accurate measurement of fuel, speed and distance.

On thing I am sure of, she will do a whole lot better in "real world" cruising than a lot of production boats - you just have to read some of the reviews where they say 3-5 liters a nautical mile is economical cruising. And I think she will look a whole lot better doing it.

Regards,

Graeme
dobsong@bigpond.com

PS email me for more details on the $$ for Celery Top

[Boston]

Originally Posted by rwatson

Thanks for that info. If you get the chance anytime, I would be interested in the cost per cubic metre. I costed Plantation Kiri recently - its over $4000 per cubic metre.

holly empty wallet bat man
you folks pay a fortune for timber down there

1 cubic meter = ~27 cubic feet
1 cubic foot = 12 board feet
12x27=324 board feet
$4,000/324=~$12.35 a board foot
dam
you guys would die if you knew how cheep wood is round here

[rwatson]

Originally Posted by Boston

holly empty wallet bat man
you folks pay a fortune for timber down there

Yes, its exciting, isnt it! Mind you, these are premium boatbuilding timbers, and Kiri is plantation grown.

The next step down "malaysian red cedar" is about 2/3rd the price, but destroys rain forests and OranguTangs.

By the time we ship timber from you to me, take into account the exchange rate, that makes it even dearer.

How about a couple of Care packages :-)

[dobsong]

Originally Posted by Boston

holly empty wallet bat man
you folks pay a fortune for timber down there

1 cubic meter = ~27 cubic feet
1 cubic foot = 12 board feet
12x27=324 board feet
$4,000/324=~$12.35 a board foot
dam
you guys would die if you knew how cheep wood is round here

Yes it hurts when you pay around $Aus100 a metre for 240mm x 42mm dressed hardwood and get told thats a good price! Makes you think about all the really great Australian hardwood that is chipped and sold for a few dollars a tonne.... but thats the "economic rationalist arguement that has enamoured our policy makers here! Let the buggars charge what the market will pay (rather than what it costs.... and because we are a captive audience we pay... and pay... and pay

[dobsong]

Originally Posted by rwatson

Yes, its exciting, isnt it! Mind you, these are premium boatbuilding timbers, and Kiri is plantation grown.

The next step down "malaysian red cedar" is about 2/3rd the price, but destroys rain forests and OranguTangs.

By the time we ship timber from you to me, take into account the exchange rate, that makes it even dearer.

How about a couple of Care packages :-)

Kiri a premium boatbuilding timber?? Strange I'd never considered that to be the case.....

[Boston]

not sure what shipping costs but I could organize a container in about a heartbeat of any north american hardwood you want
about the only ones I dont have a handle on are live oak and black Locust
everything else this new mill I been going to has got it
and dirt cheap
most in clear premium is $2 a foot
cherry and black walnut is $4
half that for lesser grade lumber

white oak is my personal fave which I got for $1.50 a foot just a few months ago
they cut heavy at around 5/4 or 9/4 on the white oak

they will plane it for you if you want to avoid shipping mill but I prefer to mill my own when Im ready to use it
course your paying for that shipping
I think planing is C 0.20 a foot

the mill is stacked to the gills with lumber at the moment
if you guys wanted any large quantity Im sure I could do even better than that

give me a species and a quantity and I can get you a quote tomorrow
I gotta call em anyway so its no big deal

I wonder how much a container can hold

[dobsong]

Originally Posted by Boston

not sure what shipping costs but I could organize a container in about a heartbeat of any north american hardwood you want
about the only ones I dont have a handle on are live oak and black Locust
everything else this new mill I been going to has got it
and dirt cheap
most in clear premium is $2 a foot
cherry and black walnut is $4
half that for lesser grade lumber

white oak is my personal fave which I got for $1.50 a foot just a few months ago
they cut heavy at around 5/4 or 9/4 on the white oak

they will plane it for you if you want to avoid shipping mill but I prefer to mill my own when Im ready to use it
course your paying for that shipping
I think planing is C 0.20 a foot

the mill is stacked to the gills with lumber at the moment
if you guys wanted any large quantity Im sure I could do even better than that

give me a species and a quantity and I can get you a quote tomorrow
I gotta call em anyway so its no big deal

I wonder how much a container can hold

What about Chamaecyparis nootkatensis (Yellow Cedar, Alaska Cedar, Nootka Cypress)? Would have to be a 40' container (to get the lengths that are useful) so I guess we are talking about a lot of timber. If sawn it would need to be 2" thick and a reasonable width say 6" at least (8" - 10" better) so it could be ripped/milled here.
________________________________________

[rwatson]

Originally Posted by dobsong

Kiri a premium boatbuilding timber?? Strange I'd never considered that to be the case.....

Oh yes, nearly as light as balsa, close to WRC for strength, virtually rotproof (like Huon Pine) but hard enough (like Celery Top).

When the Plantations get large enough, and the price is driven down, we may be able to start building guilt-free wodden boats again.