Building 23' catamaran. Build updates

[chris69]

Id say that was the hull weight not finished weight other designers do the same thing because every build of a plan is out of there control with the fit out.

[stevemid]

Looks good mate!
astonishing though that a naval architect could miscalculate the displacement by about 80%-who was the designer?

My sentiment exactly unless there is some difference between what it weighs on the scales and the displacement calcs. I gave the designer the actual measurements of where it sits on the water at BH2,3&4. He calculated that on average it was 17mm low which at that level weighs an extra 122kg. The motors I put on weigh 23Kg X2 more that his "as designed" motors

Steve
PS Actual weight 1260 Estimated displacement 750 (before personal allowances) 1-(750/1260)=40%

[stevemid]

I drove the boat down from the Hawkesbury to Sydney yesterday. It was a very confused sloppy sea. I tried it for awhile at 8-10 knots but found it much smoother around 20. While still in some smooth waters inside I took some performance readings.
RPM Knots Litres/hr

1000	4	2.6
2000	7	7.1
2500	9	8.6
3000	12	12.4
3500	15	15.7
4000	18	18.7
4500	20	24.7
5000	23	29.8
5500	25	38.1

Weight as Tested

Hull 1060

Motors 242

Driver 88

161L Fuel 114

100L Water 100

Total Wt. 1604 As Tested Neutral trim (forgot to trim out for the tests) And here she sits in Sydney. IMG_1911.jpg

[myusernam]

waterline looks ok and good that the motors trim out. 1nm per litre with twins have got to be happy with that.
pretty good how everything is done. Lots of builds i would imagine there would be half finished stuff (like a house) that you would get around to one day. please post up some usage pictures of you enjoying your hard work!

[Chimo]

Steve

Looking great.

Good to get a set of test figures in neutral position so you can compare trimmed position to known numbers for a comparison.

Is the water level above the antifoul in the aft regions?

Where did you park the S & S 34 or is she gone?

Cheers
Chimo

PS I'm guessing trimmed out around 4250 revs for 20 Kn for 20 lph

[Fed]

How do you know it was in neutral trim?

[The Woo]

Steve, are you calling trimmed all the way down, or in, "neutral trim"?

Cats are very particular to how they are trimmed, despite what some egg-spurts on here will tell you. They respond well to outboard trim, and lateral trim too can really fine tune them in certain load/wave/wind conditions.
Being a sailing man, you will no doubt be well "in-tune" to how a vessel feels underneath you. Therefore I'm sure some more time on the water in your new pride and joy will see you getting the hang of it in short order.

[stevemid]

I'm calling neutral trim when the motor is plumb...not tilted in toward the transom, and not tilted out. At that point, my trim gauges show 1 bar. Trimmed out, where the Yamaha tech said the motors liked to be, (above 20 knots on calm water) the gauges show 3 bars. In the slop yesterday I went to 4 bars and that seemed to improve the ride a bit. BTW My Yammie handbook says not to adjust trim under power. Can that be correct?

Today I tapped into my fresh water system and set up a hose to flush the engines. I forgot my Salt-Away up in the Central Coast, so the 20L tub idea with a reusable Salt-Away solution will have to wait till I get a lift up to pick up my car and begin to migrate some of my stuff back to Sydney.

I also motored down to Middle Harbour today to check on Lorelie and do a bit of tidying up prior to putting her up for sale.

So I'm still busier than a one armed paper hanger and longing to put my feet up in the cockpit with something cold and gold in my hand.

The antifoul line at the stern is maybe 5mm above the water. I'm going to have to add to that, probably at the 20 hour service.

[Chimo]

BTW My Yammie handbook says not to adjust trim under power. Can that be correct?

That does seem unlikely but maybe Yamaha uses different duty trim tilt rams on the smaller motors. Be a real disappointment if its correct as it sure would make it hard to get the best out of the motors and the boat.

Maybe Yamaha will comment?

Cheers
Chimo

[fisho64]

PS Actual weight 1260 Estimated displacement 750 (before personal allowances) 1-(750/1260)=40%

750/1260 is actually 60%

[Lovey80]

Bloody good job there. Im betting once you fine tune her you'll get a combined fuel usage of around 1.4nm/L.

You are a braver man than me. There is no way I could spend 2 years and all that money on a beautiful machine like that and then leave it sitting in the elements like that.

At the 20 hour service you could do a 50mm "Plimsol" line above your current bottom paint in a different colour like red and it will look like it was always meant to be like that.

[Fed]

I'm calling neutral trim when the motor is plumb

How do you know it was plumb?

My Yammie handbook says not to adjust trim under power. Can that be correct?

I think that refers only to the cowl mounted switch to lessen the chances of falling overboard.

You have to remember they're not real bright, here's a gem straight out of the book.

To return the outboard motor to the normal running position, press the power tilt & trim switch and slowly tilt the outboard motor down.

How does that work I wonder?

One thing that jumped out at me when reading the manual was the carbon monoxide warning, you should be very careful with that because of the big cabin sucking fumes back.

[stevemid]

How do you know it was plumb?
I was going to add, "to my eye" but didn't. Then I was going to say that I had calibrated it with a spirit level; it would have been a good rejoinder, but I didn't do that either.

I think that refers only to the cowl mounted switch to lessen the chances of falling overboard.
yes, you're right. I re-read the manual and it referred to cowl mounted switches.
You have to remember they're not real bright, here's a gem straight out of the book.

How does that work I wonder?

One thing that jumped out at me when reading the manual was the carbon monoxide warning, you should be very careful with that because of the big cabin sucking fumes back.

I've been running with the main opening hatch and the two forward facing smaller hatches open in the "vent" position. This forces air into the cabin underway which is needed to keep cool and should, I think, overcome the vacuum effect. Running with everything closed you don't even get the sense of moving--more like being in an isolation chamber, which will be nice in winter, I'm sure.


​Steve

[stevemid]

Bloody good job there. Im betting once you fine tune her you'll get a combined fuel usage of around 1.4nm/L.

You are a braver man than me. There is no way I could spend 2 years and all that money on a beautiful machine like that and then leave it sitting in the elements like that.

At the 20 hour service you could do a 50mm "Plimsol" line above your current bottom paint in a different colour like red and it will look like it was always meant to be like that.

Unfortunately, I need the anti-foul higher. Sitting on a mooring, wave slap tends to keep the sides wet a few inches up from the water, and that with the sunlight soon turns the white to green. I'm weighing up raising the antifoul up 70mm at the stern, then snapping a line to the point where the planing strake curves up at the bow. I don't think the introduced angle would be noticeable, and I think forward of that is already high enough but I'll wait to see how it looks when I get the forward area fitted. There's still a bit of weight to come there and that may lower the front and raise the stern a bit, but I'm guessing I'll end up raising the the whole thing.

As far as leaving her to the elements, I've only ever had the sailboat on the mooring so it doesn't seem so harsh, but now I do find myself thinking about motor covers and shadecloths for the windows....we'll see.

[Chimo]

Hi Steve

Glad the trip to the smoke went well. Wouldn't window covers at least be worth it if only to keep prying eyes out from a security point of view?

I am a bit like Lovey 80, were it my blood sweat and $s I rather see it up on a trailer as it was for transport or at least under cover and some security on racks when not in use. At least you know who has some experience building what you need and can knock you up a trailer. Did it work OK by the way?

Cheers
Chimo