45' solar catamaran

Sorry I should be clearer, it would be your designed protective enclosure sitting inside the tank. It just seems like it would be a convenient option from a construction stand point, and since you asked about construction I figured I would mention it. There should already be supports in the hulls for the diesel tanks. Just may need to be reinforced for the heavier batteries.

 

Good point. Can't wait to remove them an see how it's build.

 

After boat flip and full immerge . I think your project going more interesting .
What kind of batteries are you use .

 

KISS . Good point.

 

8-10 ton is way too much . For me. Best way is check those VW at different rpm vs speed achieved . And how's upwind (no mast) and you will see how it handle.
I feel insufficient power of e-m .
Propeller efficiency average 10kg/hp. If you use very low pitch will be more but speed will be limited.

 

Have you done a final weight, based on some fair assumptions about current weight plus/minus changes?

For example, say she is currently 11,500 pounds with 80 gallons diesel and tanks. Less the diesel and tanks is say -640 pounds plus two batteries of ?1000 pounds plus solar and frames and controls say 1000 pounds? Minus engines of say 300 pounds? Plus electric motors, etc.? My numbers are dartboard outer edge, but my gut hunch is you are adding lots of weight. Maybe 2000 pounds?

 

I don’t think your number of 10kg is at all accurate for this vessel.

 

According to googles each engine without transmission is 485 lbs each.
VOLKSWAGEN MARINE SDI 60-4 59HP https://www.maritimepropulsion.com/directory/product/volkswagen-marine-sdi-604-59hp-129772

 

Weight of the Vw doesn't matter .

 

Why not for this vessel ?

 

You remember post #9 of this thread. ''That give me a displacement of 3.5 ton (7770 lbs) at water line per hull, so 7 ton for the boat.''
That is the only guess weight I have, so if I remove 2 engines and add a lot of stuff, I call this 8-10 ton at the moment.

 

I think in case of big trouble like that the boat will be lost. But I want to be sure that the batteries will not catch fire few seconds after water intrusion or be sure that the battery will not move in case of terrible even.

I bet many people are not ready to read this and could be fear... I plan to use EV battery.
NMC chemistry to be exact and after looking at Mustang Mack-E battery, VW ID4 battery, Kia EV6 / EV9 / Niro battery and even Tesla 3 LFP battery, I think I found the best candidate.
The 8S modules inside Cadillac Lyriq / Chevrolet Blazer EV / Equinox EV / Honda Prologue are very nice.
They are energy dense and are fairly easy to put in a series/parallel configuration who can give 16S with 5 modules in parallel, so 58V nominal and 1400 Ah.

Now why EV battery modules?
Because they are high quality, automotive grade, affordable (when used) and I'm used to design with this kind of module since a while now.
Those EV (Lyriq, Blazer, Equinox, Prologue) are fairly new on market (2023-24), but I can count on multiple distract drivers/bad drivers to find many batteries at scrapyard next year.

 

I have a semi-planing cat and probably weigh about 11,000 pounds and going 21kts at wot with two 90hp Yamahas.

So figure what maybe 1/4 throttle, say 45hp for hull speed.

11,000 pounds is 5000kg

5000kg/45hp is more like 100 kg/hp

Have I misread you?

 

First you need to know what the resistance is for your boat at that speed. The propeller will be whatever the calculations show it needs to be. Diameter and pitch alone are not enough. Number of blades and blade area must be included. If you have previous measured data for power vs speed, that can be used instead.

 

Yes. Probably my chinglish. I mean average thrust of the water prop. Air prop static is 2kg/hp . Only for starting point of any considerations.