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BOAT WONT GO ABOVE 14KT

L

lugnutdan

Contributing Member
"PLEASE HELP:
I have a 1996 t

"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??????"
 
"Dan,

By your diver saying

"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."
 
"Thanks al I just changed all

"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????"
 
"Dan,
Yes they can but typica

"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."
 
"I can attest that a out of wa

"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."
 
"Fred I have not decide what w

"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????"
 
"I use an optical tach on my b

"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"
 
"That's were I got mine, t

"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."
 
"I will be honest i have no id

"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."
 
"In essence, an optical tach i

"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."
 
"Dan,

Mark tells it like it

"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."
 
"From Pasco's 10.8m writeu

"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?"
 
"Nice Find Dave!

I thought

"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."
 
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