Props & Speed

[sbeer]

If you are over propped as much as you say, then you should be bellowing black smoke out the back like a garbage silo. Get a cat tech down there and verify your fuel settings. You also could have a govener[?] issue. They are spring actuated. Sometimes the springs go. If you ask me I would have the govener looked at. Sounds like it isn't reacting to load. The more load that it senses, the more fuel it delivers. Mike My spelling su#ks Mike Lawrence 81 sportfish 33' shot'n'beer

[franklyprice]

Robert, If the growth effects the speed it will effect the RPM. The two are connected like the tires on your car to the road. At any kind of speed the prop slip is pretty minimal, so maybe be a little careful taking too much pitch out. Frank Price 1987 SF"JEANNE CLAIRE' Rowley Ma [img]http://www.bertram33.com/photogallery/p ... Claire.jpg[/img]

[Sean B]

quote:Originally posted by robert watters reading these earlier posts I've come to the realization that growth on the bottom would have affected speed of the boat but surely wouldn't have affected the ability of the engines to turn the props at max revs Trust me, growth can and will do just that. I took my under-propped boat out dirty once and could only turn about 2550 at WOT, when I usually get 3050. Don't underestimate the effect a dirty hull and running gear can have Sean Burlingham "Island Time" 1987 Bertram 33 SF Melbourne, FL SBurlingham@cfl.rr.com

[sbeer]

You are only getting 2100 rpms, underload, and 17knots. If the bottom was the culprit, wouldnt that cause an overload? When a diesel is overloaded it will start smoking black smoke. Crusty bottom, bent props and so on cause overload issues, which means smoke.The turbos spool up to add more air to mix with the fuel that is being injected. If you are adding fuel but the motor isnt turning up, exhaust causes your turbo to spool up, then there's not enough air to fuel which causes smoke out your exhaust. Sounds like your not getting fuel or enough of.. You havent said anything about getting smoke. That tells me that the motors are not reading load. When the govenor starts to feel load it adjusts fuel to compensate. This will not happen at wide open at the dock. The 21x22 props, in my opinion, are right where you need to be. Do you have pyro or boost gages? Correct me if I am wrong. Maybe I am looking at it the wrong way This is just my take on it. I went through alot of issues with smoke and overload. It took me a year and ahalf to get mine squared away. Mine are running right where they should now. Mike

[robert watters]

No black smoke at all; a lot of gray at start up but pretty much disappears when warm, though there are whisps when its put to the pins. You're right though; if the props had too much pitch you'd expect the engine to be over-loaded and the most common sign of that is black smoke. I don't have pyro or boost guages; maybe I should have the cat mechanic take a run, the prop ding isn't bad, but perceptible when you run your hand over it.

[mak6190]

Hello Robert, Props are a big issue. The Gear that you carry along hidden inside the side pockets or inside under the galley also will tax your expected cruise. My 1982 SF with Cat 3208's 275 Hp has the 1 3/8 " shafts with the MG502 Gears . I have a 70 gal water tank and a 315 gal fuel tank, with a 6.5kw Phasor Generator in the mid section of the boat . I am currently running 3 bladed 21X21 Federals. I thinks they are the original props that shipped from factory with my 82 SF ( show in the original boat manuals). They are very heavy and have thick blades.One Federal prop weighs about as much as the 2 DynaJets , that's a big difference ! I have two pairs of props, the DynaJets and the Federal Equipose. The 3 blade DynaJets were 21X22 with a cup were much better performing than the Federals. I have never been able to do better than an 18.7 kts cruise at 2350 rpm with the DynaJets. WOT loaded down I could do almost 25kts WOT but the engines would not turn the correct rpm, they would not pass 2600 rpm wich would make me over proped and prone to reduce engine life, unless I ran with less than half a tank of fuel, little or no water in the tank, then I would see a close to 2800 rpm top. As the engine hours grow you will need to pull off a pitch or two. I have changed these prop pitches over 15 times in the past 3 years and all I can say is that the DynaJets were probably the best all round perfomers @ 21X22 with a cup. I have put just over 1000 hours on the Cats in the las 3 years with no major issues, just oil changes , filters and water salt water pump rebuilds. One of my DynaJets props is not fit to be used any more and I have as a back up spare becuase one of the blades had a hairline crack at the hub and the prop tech. recommened that I not use it any more. So I use the Federals @ 21X21 no cup. They perform 18.2 kts @ 2500 RPM and at WOT the boat will do almost 22kts running almost 2950-3000 rpm. When the boat is fully loaded it will still hit the 2800 rpm which is what everyone looks out for. If you paint the props you will loose 1/2 kts performance. If you don't paint the props you will have to clean them once every 15 days ( scrape them with putty knife and sandpaper). I do the second becuase I have a guy who gets in the water and clears them for me. Some people put black plastic bags to prevent the props from fouling up, and it works. We can still use SeaHawk ( hard) paint down here in Venezuela. It last anywhere form 12- 14 months. The hull just needs a little cleaning around month 8 ( just sea weed , no barnackles). Alot of the anti fouling paint performance has to do with water temp. and also where the sun light hits the hull the most. The more Sun you get the more the fouling ! I Hope this information is of help !

[robert watters]

Put the boat back in the water today with a new bottom job and the speed improvement was dramatic - the boat will now hit 21 kts but at WOT the engines are only turning 2300 rpm , so it's clear that I;'ve got to reduce the pitch. I think I'll order a pair of Dyna Jets as a spare set and see how that works.

[Sean B]

If you've still got the 21x22 props, I think you should be doing WAY better than that 2100 RPM. Something else is going on, maybe one of you engines isn't working as hard as the other. My props are 20x22, smaller diameter but same pitch as you and I'm underpropped. Now you've eliminated the bottom but I still think some other problem is slowing you down. I bet you are dragging one engine with the other. Do you notice more smoke coming from one engine? When you had the boat out, did you have the props checked, at least visually? A bent blade can do a lot too. I think there is a process detailed on Boat Diesel, to crack injectors, one at a time, to see if all cylinders are firing on the engine. When you stop one cylinder at a time from firing, you should notice the engine RPM and running sound change. If you crack an injector and nothing changes, you found a deadbeat cylinder. Probably not what you wanted to hear, but it's also just a semi-educated guess. Sean Burlingham "Island Time" 1987 Bertram 33 SF Melbourne, FL SBurlingham@cfl.rr.com

[dougl33]

Sean, In an earlier post Robert said that both engines were hitting wot no-load of 3050. The bottom is clean, and the props seem like they're the right size. Could this be a transmission issue? Just thinking out load trying to figure what else it could be that's keeping the rpms so low. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA [img]http://www.bertram33.com/photogallery/p ... sabeth.jpg[/img]

[Sean B]

If an engine is running on seven cylinders, would it necessarily have a lower no-load WOT RPM? I don't know for sure but I suppose it would still hit the rated RPM, because the other seven working cylinders would still be plenty capable of doing that. The "throttle" on a diesel is really just a governor setting, your throttle setting is just telling the engine to "go to this RPM," and it automatically uses as much fuel as it needs to get there. Seven cylinders could still hit 3050 without a load, but you would certainly be missing that 8th one under a load. I may be wrong because I'm not speaking from experience here, only logic. Would make a good boatdiesel.com topic but I'm already up too late, and once logged in I can't spend less than 2 hours there. Sean Burlingham "Island Time" 1987 Bertram 33 SF Melbourne, FL SBurlingham@cfl.rr.com

[Sean B]

Hey Doug I was so busy yacking about a missing cylinder that I forgot what you suggested. Yes, a slipping gear would certainly slow you down too, although I'm not sure how you test for that. Maybe run the boat at WOT, one engine at a time (with the other running in neutral to keep oil circulating in the gears), and then compare the results? I'm not sure what that would tell you, except which engine is a problem (or if both runs are both same then likely neither one is). I don't know how to diagnose a slipping gear but I have heard of the problem before. Sean Burlingham "Island Time" 1987 Bertram 33 SF Melbourne, FL SBurlingham@cfl.rr.com

[sbeer]

A bad injector would make the boat run as if you had something on the prop. Vibrate. Running one up in gear and not the other would be severly overloading that motor and could cause some really bad things to happen. The problem seems to be a loaded problem. Have props been scanned and found to be identical? Could be a govenor issue. That is load related.Your not getting smoke so your not getting to much fuel to cause the smoke which would indicate the overload. The govenor springs might be lazy or need to be replaced. I would get a mechanic down to look at it. If it go's you may only be able to achieve enough power to dock it. Mike

[Brian Davin]

I had a problem leaving Nantucket last summer when the boat wouldn't come up to cruising speed with both Tachs at 3,200 rpm. After spending a few hours with a mechanic testing a variety of things (for $289) he came to the conclusion that one tachometer was not reading properly and though the tach said 3200 rpm's on that engine, it was only actually turning around 2,000 +/- rpm's. I proceeded to run the boat to Cuttyhunk, operating that throttle by sound matching to the other engine. Half way to Cuttyhunk the tachometer suddenly started working properly and I found that I had set the throttle to within 50 rpm's of the other engine (not bad I thought). Something to think about anyway. Brian '90 Bertram 33' FBC Never Say Never Guilford, CT (Homeport) Kinnelon, NJ (Home)

[Sean B]

quote:Originally posted by sbeer Running one up in gear and not the other would be severly overloading that motor and could cause some really bad things to happen.A two-minute run on one engine to see what is up isn't going to hurt anything. Of course I wouldn't do it all day. The overload-related engine problems you hear about are because guys are putting 100+ hours on overloaded engines, usually because they are over-propped. Your engines will tell you when they are overloaded: black smoke. I agree though, governor and maybe fuel injection pump may be causes. I assume racors and secondary fuel filters have been changed recently? I still think it would be a good idea to try one engine at a time, to see if you've got a engine lagging, and if so more importantly, WHICH one. Sean Burlingham "Island Time" 1987 Bertram 33 SF Melbourne, FL SBurlingham@cfl.rr.com

[robert watters]

I'll do the one engine test this weekend. The port engine tach stopped working on last run (Aetna digital running off the cat 3208's) and its not the head unit, so have to check wiring and then the little generator that sends the digital signal to the tach. Boatyard also told me that the port shaft measures .025 out of true, but no vibration evident. The saga continues...