How is Max HP rated????

[Dunco]

Just would like to know how boats that are around 15 ft can have a 75 or 90 hp or more strapped on the back.

Is it because of the structual design ie. Pod on the back?

The boat I'm getting built is a 4mm bottom and sides, plate boat with no pod.

The builder has rated the Max HP to be 70hp and the boat unloaded wieghs about 425kg.

If you add Electric motor, Dual Batteries, Esky, Safety gear, Tackle and Two blokes on average. I'm sure I'll be near 650kg-700kg. Then add the motor wieght. All this in a 4.6m Centre Console.

What can I ask my builder to add to make this boat handle a 75hp+????

Also would be interested in what size motor members would recomend for a good fast ride?????

Attachment 9713Attachment 9714Attachment 9715

[Woody01]

Hi Dunco,

Who knows how they rate max HP after what I have just found out. (My recent thread on Max HP ratings vs Actual motor on my boat).
When I questioned my boat manufacturer as to why my 5.8m ally was only rated to a max of 140HP he told me that I could easily run a 200 on it, and that they stamp them low to cover their backsides!
Go figure!???

cheers,

Woody.

[onerabbit]

Interesting Question,

my 30 odd year old seafarer is rated to take 175hp, which in its day may have been ok, hull wouldn't touch the water with a modern one.

Muzz

[Chimo]

Hi Docco

This has been posted on here and elsewhere a number of times as an example.

Hope this helps

Chimo

Re: Australian Standards #AS1799.1
Australian Standards Calculation AS 1799
Length of boat X Waterline beam width at transom X 16 less 67 then X 1.34 = hp you can use on your boat.
So an example might be
6m boat X 2.14m =12.84 X 16 =205.44 less 67= 138.44 X1.34 =185.5 hp

There is also speed tests on water to be done with right angle turns to be performed successfully at full speed etc

[Dunco]

OK as per Chico's Calc =

4.6m x 1.8m = 8.28 x 16 = 132.48 - 67 = 65.48 x 1.34 = 87.74HP

So when I talk to the builder toomorrow I'll ask him nicely to stamp a 80hp plate on.

I'll let ya's know

[FNQCairns]

Hey Muzz todays engines are overall slower than those of the past, di's esp, the mercs of days gone/almost gone by especially, although the performance versions of the optimax does a good job of getting close.

I just love marketing

cheers fnq

[Chimo]

Sorry Dunco /(vice Docco)

Whos Chico ?

Cheers
Chimo

PS I'd go for an 85HP Plate

[Spaniard_King]

Chimo... Why do you think my new 6m boat is rated to 250hp then and it's built to survey?

[Chimo]

Hi Gary

I've no idea!

What happens if you apply the Aust Standard formulae to your setup?

If its got a broader beam the numbers may be higher, just a thought tho.

Cheers
Chimo

PS On the same vein my 6.2 Vag is rated to 230 HP so maybe someone is not useing the formulae correctly.

[Spaniard_King]

Chimo,

I beleive its a little bit more than just the formula.... from a boat builder its all to do with stringers and strenght.. nuthing I know anything about.. the formula may just be a guide for existing boats IMO

[Chimo]

Hi Garry

I'm not an expert on this either but the Aust Standard that specifies all this includes the high speed turns etc so I guess they apply a "safety net" to the fromulae.

Perhaps if the thing turns over on the high spped turns someone stuffed up and its either back to the drawing board or fit less HP to have a fudge factor built in.

I might ask Lindsay when I see him next.

Cheers
Chimo

[Dunco]

Sorry Chimo just havin a go at your typing

I think I might start for a 90hp plate then see If he'll barter down to a 75hp.

I can get a good price on the 75hp Honda ($13500 fitted) so I'm going to twist the dealers arm for a price for a 90hp Honda. Same wieght just heaps more fun!!!

What would be a good price? anyone.