My 1975 36C needs to go on a diet! Travelift says 27,000lbs+!

[bhostrawser]

Ok, I think this explains why we are dogging it with a 16kt cruise and 20kt top end!

Can anyone else running 3208T @320hp weigh in (pun intended, sadly) on what sort of performance the are getting, and what sort of setup you have, I've got the 2:1 506 TD, 1.5" shafts, way too much weight.

I am aware that people prefer > 3:1 safety factor, I'm also aware that Slane has done a lot of these repowers and never had an issue with the shafts. I'm also aware that people prefer inline 6's that lighten the boat and give more engine room space. Frankly, I prefer greater safety factors and smaller, lighter, more powerful engines also(to a degree). However, changing the shafts and repowering are just not options right now, so we are trying to do the best we can with what we have.

I just hauled yesterday and the props are a bit dinged up and have some electrolysis going on. I'm waiting on a callback as to their exact pitch, but I think they are close to the stock size of 22x22 dyna quads?(He just called, 22xSomething, each blade is different, from 22 to 26"!) I'm expecting to have to buy new shoes, and want to drop some weight to get a bit more performance and a touch more pitch.

I'm running the numbers at boatdiesel.com, and I'm not sure what to put for hull type, slow or med planing? lwl approx 33'?

As is, the engines are getting to just over 2800rpm at max throttle, so without losing weight, we aren't going to get more performance out of the boat, so keeping the approximate prop setup would be required. However, I'd like to get this fatass up on a plane at cruise, so, what should my target weight and prop setup be?

I realize that I won't be a speed demon with this setup, or this boat, I just would like to get it somewhat reasonable and I'm sure some people out there are running these Cats with better performance? Or, maybe not?

Thanks in advance,
Brent

[Avenger]

Ahhh, the definition of "on plane" strikes again. If you're cruising at 16 kts you're on plane. Pet peeve of mine, sorry.

Now on to your problem; Whatinahell do you have on that boat that makes it so heavy? My 3208s are only 260 HP and my numbers (when the boat is clean) are better than yours. I'm sure your engines can't weigh more than maybe 100 lbs more than mine. My yard's travelift won't do weight, or maybe they don't know how to interpret it, but doing the performance math says the boat weighs in at a little over 20K. Leave your anvil collection at home.

[bhostrawser]

Ahhh, the definition of "on plane" strikes again. If you're cruising at 16 kts you're on plane. Pet peeve of mine, sorry.

Now on to your problem; Whatinahell do you have on that boat that makes it so heavy? My 3208s are only 260 HP and my numbers (when the boat is clean) are better than yours. I'm sure your engines can't weigh more than maybe 100 lbs more than mine. My yard's travelift won't do weight, or maybe they don't know how to interpret it, but doing the performance math says the boat weighs in at a little over 20K. Leave your anvil collection at home.

Haha! I am sorry, I am on a plane, just a really slow one that pushes a lot of water and leaves a big wake! I understand the pet peeve, and you are right, my bad and thanks for the correction.

As far as contributors, I have a 5kw Westerbeke genset, a big old stainless radar arch, and in the cockpit I have a built in rigging/filleting station that is heavy that contains the house battery and a small freezer/ice maker. I still can't come up with that much weight though. I've been taking off as much as I can since I've owned the boat the last few months, but it had accumulated a lot of stuff over the last say, 30 years.

With the starting batteries, generator, and extra station all on stbd side, the boat lists a bit, and thats probably not helping either. Additionally, the props seem messed up enough that they are not being very efficient either. Can I ask your redux/prop setup?

Also, any strong preference for DQX vs DynaQuads?

Also, Scrod, I really like your hard top & furuno setup, that is high on our list, can I ask where you obtained them? Thanks!

[Avenger]

The "on plane" thing has to do with when a friend who's a fairly knowledgeable boater made some comment about us not being on plane when we were doing 20 kts. He was a practiced outboard boater, so his idea of on plane was closer to an airplane. Still wanted to toss him over the side though.

Nothing you're describing adds 3 tons to the boat. There's got to be something else going on here. Got a granite cockpit deck?

My props are 20 x 23 3 blades with a 1.5:1 gear. When it's clean the boat will cruise at 19-20kts. It is a little light right now being sans generator and some salon furniture, but again, not 7,000 lbs light. I have no firsthand experience to offer you on the props, sorry.

The top speed formula is: 150/(√(displacement / HP)).

So mine: √20000/520= 6.201, 150/6.201 = 24 kts, which is about right.

Yours: √27000/640= 6.495, 150/6.495 = 23 kts. If you're only getting to 20kts. It would appear you've got more going on than just weight. How about tabs? Mine can get the speed up a little in the lower end, but hamper it at the top. I also had a major issue with rudder toe-in that created quite a speed-brake. * Just saw your edit about the blade pitch issues. That's probably the reason.

Thanks for the kind words on the hardtop/RADAR. You can ask, but I can't tell you who did it. It came with the boat.

[bhostrawser]

Ok, well that is good information. It is possible the condition of the bottom and the props knocked off a couple of knots as well. The bottom was cleaned recently, but on the haulout, the yard manager said the type of spaghetti growth is slow to form, so it had not been cleaned very well, he thought it could easily take off 2-3 knots, and with the props being "uniquely" pitched per blade, I think that probably rounds out why we aren't seeing 23 kts.

As far as the tabs go, they are the only way I can get to 20kts. If I don't use them, I'm pushing 18-19kts and a really big wake. At lower speeds, they help a bit, but not a whole lot.

I should add there are probably almost 250 gallons of diesel in the tanks. I still don't see the weight adding up, though it is getting closer. I'm hoping there are some gold bricks down in the bilge somewhere.

I'll check the rudder alignment, that is something I had not thought of. Thanks!

[Avenger]

When we went to the rendezvous at Block Island the running gear was somewhat fouled which dragged our speed down. In that case the tabs would gain us a couple of knots. When she's clean and in the corner they'll reduce the top end by two knots or more.

Our fuel load didn't make any noticeable difference. We started out with about 240, burned down to maybe 60, added 70 and burned that too. Can't say we saw any speed change because of that. My feeling is that it's because the tanks are under the cockpit where the hull's best lifting surface is. So there's plenty of surface to carry the load.

[jim rosenthal]

How accurate are Travelift scales? I've heard that they vary considerably and that they have to be re-zeroed after every boat is on them, if the slings are changed. Is that true? And that even if they are zeroed they are not particularly accurate.

I find it hard to believe that your Series I 36C weighs 27,000 pounds. Is she floating on her lines or is everything including the boot stripe underwater? That is six or seven thousand pounds overweight- as much as 33% over nominal weight, maybe. You have a lot of the same equipment that other 36Cs have, and they don't weigh that much.

I think if I were in your situation, I would get the props tuned up really well, or replace them, and get as clean a bottom as you can, and get all the weight off the boat that you can, and then sea trial her again. And meantime post some photos of your boat in the water. I will agree that she is three tons overweight when I see the exhausts and everything else under water. Until then, I think maybe the scales are mistaken.

You also might check your propshaft rpm versus your engine rpm. It is possible that your gears are slipping and that even though the engines are reaching full rated revs under load that your wheels are not getting to the corresponding full revs.

[dsharp]

I would get the wheels you have re-pitched. The diameter and pitch should be stamped on the hub. It looks like the difference in props is the Dynaquads are bronze and the others are nibral. Are those engines governed at 2800? The governors may be restricting the rpms instead of the props. The 36' and 38' series one Hats were not the easiest boats to push. They were built like tanks and you pay a certain penalty for durability. Are the wheels you have now pitted or discolored?

[dsharp]

I would get them rep itched so you will know what you need when you order new wheels

[jim rosenthal]

I think WOT under load on those engines is 2800; but a call to the CAT dealer should clear that up.