Design Question on powering

[Salmoneyes]

I did a 'quick' review and
(a) That 50% increase (4mm to 6mm) in plate thickness probably did the trick re the weight matter
your disp/length ratio is around 440. A maximum should be about 350. This will affect performance and many other aspects.
(b) prop calculation looks like 22 x 15 x 3 blade - you may have to trim your 23" down a bit to avoid tip cavitation - or possibly look at a bigger reduction (2.25+:1).

Who did the design & build?

She is Bruce Roberts penned but strayed a bit. Keel was lengthened, the masts lowered with smaller sail plan, and she is too heavy.

Hull was built with a technique I was unfamiliar with but common for commercial steel fishing boats in Sweden. Can be modded to be stronger and loose weight at the same time even if only a 100 pounds.

I have access to help from Bruce but we are looking at many options to get her numbers to all jive, and I am trying not to have him redesign it multiple times.

The entire propulsion system is one way I possibly can drop 900 to 1000 pounds.

 

[Salmoneyes]

It is not a single formula per se. Which is why I have asked the Qs I have and in that order too.

So, in the absence of such, you can obtain the power/resistance from the basic particulars of the vessel using known data.

Thus you first need to establish your length - displacement ratio.

the disp/length ratio came out to to 447 using tom doves calculator.

I looked at the formulas and I am working it out on my own, but I am teaching myself the math as I go, so it is a very slow process. When I start getting a headache I go work on the boat demo..
Unfortunately, im running out of things I can do without having a master plan which Im making, thanks to help from this forum...

 

[Ad Hoc]

The disp/

the disp/length ratio came out to to 447 using tom doves calculator.

Ive no idea what/who Tom Doves calculator is.

It is a very simple calculation.

The waterline length - in metres
The displacement - tonnes

The LD ratio is thus: Length / (displacement)^1/3

That's it.

 

[Salmoneyes]

Ive no idea what/who Tom Doves calculator is.

It is a very simple calculation.

The waterline length - in metres
The displacement - tonnes

The LD ratio is thus: Length / (displacement)^1/3

That's it.

Sorry, I was referring to Gerrs formulas found in the Prop Handbook... There was more to that book then I thought originally.

 

[JSL]

Displacement Length ratio in imperial is:
D/(0.01 x LWL)^3
D = long tons (2240#)
LWL = feet
as noted in Gerr's book pg 13, and also several other books.
With your Disp/LWL ratio of 440+ you might expect a top speed of around 6.5 knots under power.