| Author |
Message |
    
danny
Member
Username: lugnutdan
Post Number: 22
Registered: 02-2009
| | Posted on Tuesday, September 08, 2009 - 10:52 am: | 
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PLEASE HELP:
I have a 1996 trojan 350 express,with twin 502 xl crusader fwc engiens it use to get 34-36 KT
cruise 18-22.
I recently had a bottom job,diver went down,the only thing he saw was approximetly,2 inches up on each prop,he said it looked like it was sand blasted,maybe went thru some sand(i never felt anything)I noe notice the boat will noy get more than14-16 kt,at 3200 rpm,nmothing rapped around props,engiens run good,any suggestios, were to start looking would be a real help,I ve had a couple people tell me to take props off and have checked?????? |
Al
Advanced Member
Username: knuckle47
Post Number: 575
Registered: 09-2007
| | Posted on Tuesday, September 08, 2009 - 11:41 am: |
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Dan,
By your diver saying the props were scuffed to about 2" it could be possible that your props have felt the brunt of the bottom and are no longer spec'd out as they were. Did you notice the last run out that it was running at the faster speeds. Logically it would seem that if all else if OK...Start with the props, at the same time check fuel filters and lines. Demands under loads are different that at the dock revving up towards redline. |
danny
Member
Username: lugnutdan
Post Number: 23
Registered: 02-2009
| | Posted on Tuesday, September 08, 2009 - 01:25 pm: |
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Thanks al I just changed all filters and did tune-ups,on both engiens.
I remember going thru some mud,about two months ago,and really didnt notice anything ,we live aboard,and really dont get it to wot, so its been some time and just noticed it last week.
would the props really cause that much of a loss in power???? |
Gregory Mrozinski
Member
Username: gpmrozinski
Post Number: 46
Registered: 07-2009
| | Posted on Tuesday, September 08, 2009 - 02:06 pm: |
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Dan,
Yes they can but typically you would feel a vibration of some sorts if the prop was out-of-wack. Any vibrations? Also try checking the shear key on the prop/shaft taper. It's a long shot but maybe the key sheared and the prop is slipping on the shaft. |
Thom Hemler
Member
Username: phoenix1
Post Number: 18
Registered: 07-2009
| | Posted on Thursday, September 10, 2009 - 10:54 pm: |
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I can attest that a out of wack prop can result in substantial drop in power, although this is an extreme case. I recently grounded my 88 Pheonix bending the props. At WOT, I could do no better than 14kt where prior 28-30kt. I did experience the vibration Greg mentions. After having it repaired, the boat returned to normal speeds at various rpm's. |
Freshwater Fred
Advanced Member
Username: fred70
Post Number: 196
Registered: 01-2009
| | Posted on Tuesday, October 13, 2009 - 09:56 am: |
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Danny, did you find out any thing solid.
Fred 156-M |
danny
Member
Username: lugnutdan
Post Number: 37
Registered: 02-2009
| | Posted on Tuesday, October 13, 2009 - 07:33 pm: |
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Fred I have not decide what way to go yet,or really what to do,ive got people telling me my transmmisions, and others telling me props???? |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 6945
Registered: 09-2003
| | Posted on Wednesday, October 14, 2009 - 07:08 am: |
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Start with props. Easier to check and far cheaper!
Jeff |
danny
Member
Username: lugnutdan
Post Number: 38
Registered: 02-2009
| | Posted on Wednesday, October 14, 2009 - 07:55 am: |
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thats the direction i was looking at ,thanks |
Freshwater Fred
Advanced Member
Username: fred70
Post Number: 197
Registered: 01-2009
| | Posted on Wednesday, October 14, 2009 - 08:04 am: |
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Is there some "inexpensive" way that lugnutdan can measure shaft RPM ?
Fred 156-M |
Al
Advanced Member
Username: knuckle47
Post Number: 721
Registered: 09-2007
| | Posted on Wednesday, October 14, 2009 - 08:51 am: |
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I use an optical tach on my boat to measure idle speed,and it seems to work very well. It uses and piece a reflective tape and after 1 year....those tapes are still in place in the bilge. Total cost $14.00 ...eBay |
makomark
Senior Member
Username: makomark
Post Number: 1660
Registered: 09-2008
| | Posted on Wednesday, October 14, 2009 - 11:54 am: |
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That's were I got mine, too. Found a 'brand name' that was used (scratches) but fully functional. I figured the scratches were well worth $35 (delivered) for an instrument with a street price of $250.
Since mass production has lowered their prices, the phototac's are cheaper/easier than pulling the props. You can also use them to see how far off your dash tachs are, too. |
danny
Member
Username: lugnutdan
Post Number: 39
Registered: 02-2009
| | Posted on Thursday, October 15, 2009 - 06:23 pm: |
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I will be honest i have no idea what these aer or how to use them ,do i under stand correctly. these will tell me wether the problem is my props or transmisions. |
makomark
Senior Member
Username: makomark
Post Number: 1672
Registered: 09-2008
| | Posted on Thursday, October 15, 2009 - 06:47 pm: |
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In essence, an optical tach is a laser diode, a receiver/detector and some electonic circuitry to do some counting.
The laser beam bounces off the reflective tape Al mentioned and the 'pulse' is captured by the receiver. The circuitry figures out how often the pulses come in and drives the display in units of RPM.
You measure the shaft speed and commpare it to the engine rpm, adjusted for any reduction in the gear.
If the engine is turning 3000 rpm and your gear is a 1.52:1, the shaft should be spinning at 1974 RPM. Anything significantly less and the clutches are slipping. If it is ok here, try a higher RPM. If the shaft is spinning at the correct speed and the boat is 'slow', the prop key is the next likely place to look.
It will take longer to read this than to do the actual measurement. |
Al
Advanced Member
Username: knuckle47
Post Number: 725
Registered: 09-2007
| | Posted on Thursday, October 15, 2009 - 07:03 pm: |
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Dan,
Mark tells it like it is. Mine came with about 3 feet of this 1/4" reflective tape. I figured by now it was gone and fallen off, but when I tuned up these engines 2 weeks ago after 1 year of placing the tape on the pulley, they were still in place. You simply bounce the laser beam off of the spot you placed the tape and ...presto!...rpm readings. |
diver dave
Advanced Member
Username: diver_dave
Post Number: 458
Registered: 08-2008
| | Posted on Friday, October 16, 2009 - 08:58 am: |
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From Pasco's 10.8m writeup:
Unfortunately, the hull shape won't quite give the performance of a Bertram or Blackfin, but its adequate in my view to handle the moderate stuff. With 350 hp Crusader gas engines, the speed is probably not what you'd like it to be as it tops out at around 22 knots with a clean bottom. Another 50 hp would do wonders - to the speed and the fuel bill. With these engines, there's adequate space in the engine room. But with the optional 300 hp Detroit Diesels, its badly cramped and the boat becomes grossly under powered to boot. That's the one big-time drawback with this boat -- you got all that wonderful interior space at the expense of engine room space. And as near as I can tell, Cat 3208's will not fit in this one.
Considering the 8,000 lb. difference in weight with the Bertram 35, we're wondering where the loss of speed came from because the B-35 will do about the same with those engines. We'd have thought that she'd get up to at least 25 kn. at 4000 RPM on engine rated at 4000 to 4400 RPM, and wondering about the 1.88:1 Borg-Warner gear boxes. Seems a lot of reduction for a 15,000 lb. boat. Would it do better with 1.55:1? |
makomark
Senior Member
Username: makomark
Post Number: 1678
Registered: 09-2008
| | Posted on Friday, October 16, 2009 - 10:01 am: |
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Nice Find Dave!
I thought 35kt on a NA gas powered 35' was a bit optimistic, too.
I'd bet the 1.88 gears make the engines last much longer than the 1.52's would; at the expense of top end speed. |
