Prop Problem

[hugues1811]

i bought an endeavour 40, the engine is a perkins 4.108, or a 4.99 rated 45hp at 3600rpm. I can only reach 1700 rpm full throtle and the boat go a little bit over 6 knot. the prop is 17/16 and the hurth150 transmission have ratio of 1.875 forward. In the manual of the boat they say that is the prop for the boat, but the rpm is really slow and 2 different prop manufacturer advise me to install a 17/10 and i just gave them info about the engine and the transmission, who is wrong ??? anybody have a similar boat can tell me wich prop to use ???

[fstbttms]

Considering that the boat currently wears the prop that the manual recommends and does not perform well under power, I think it's safe to assume that the manual is wrong.

[mesquaukee]

Does the engine rev up to 3500 in neutral, prop shaft rotates freely, clean prop, all the usual, etc.
If all thats good you are killing your engine with carbon deposits. You are putting a lot of strain on the crankshaft etc as the engine is maxed out at 1700. The maximum amount of diesel is being injected and theres not much air to burn it.
A 17/10 has about 2/3 of the bite as a 17/16. It will be better than you have now. Props are a pain in the butt to get right. The best way is to borrrow some and try them out.
Leave a little bit of a power researve for when there is square seas and a headwind.

[David M]

If your engine is healthy, then you are way over pitched. Your engine will have a much shorter life if you leave it like this. Additionally, your engine is not reaching full horsepower if it is not being allowed to reach the higher RPM's

[osirissail]

I have dealt with Perkins engine for a long time and would suggest that maybe you do not have a prop and engine speed problem - but instead a tachometer problem. Normally the tachometers on Perkins are electronic working off your alternator. It is a very unreliable system but very economical to put on a boat. Get or borrow a stroboscoptic RPM meter. This is an instrument with a meter and a stobe light that shines on your front of the engine pulley. Normally you have to adhere a little piece of reflector tape on the rim of the pulley that will reflect the strobe light as the engine rotates. This will give you an authentic RPM of the engine which you can compare to the electric alternator tachometer at the helm. Electric tachs come with a little rotatable selector on the back that is labeled 2 or 4 or 6 or 8. You rotate this selector switch to progressively increase/decrease the displayed RPM calculated from the pulses that the alternator puts out as it rotates. A faulty alternator will give your Tach wrong information.
If the optical tach and the normal helm tach are close to each other then you have a different problem - probably a prop problem.
If you are getting 6 kts out of a 40 ft boat at half throttle that is pretty good. If the prop is too big you will also get black diesel smoke out of the exhaust as the engine labors to achieve full RPM's but cannot. If you get to maximum book rpm's easily/quickly with the prop then the prop is too small. You would normally find a used prop shop and borrow a variety of pitches in your prop diameter/shaft diameter and test each one to see which one gives you near max speed at 3000 rpm.
For the Perkins 4.108 normal max rpm's is 3,600 and maximum continuous operating rpm's is 3,000 rpms. Normal cruising is about 2200-2400 rpm's. With a little experience you can hear the "sweat" zone for cruising rpm's. There is normally a definite change in tone and the feel of the boat vibration between optimum cruising rpm and the higher rpms.

[captmick39]

Originally Posted by osirissail

I have dealt with Perkins engine for a long time and would suggest that maybe you do not have a prop and engine speed problem - but instead a tachometer problem. Normally the tachometers on Perkins are electronic working off your alternator. It is a very unreliable system but very economical to put on a boat. Get or borrow a stroboscoptic RPM meter. This is an instrument with a meter and a stobe light that shines on your front of the engine pulley. Normally you have to adhere a little piece of reflector tapeOr a brush stroke of "whiteout"on the rim of the pulley that will reflect the strobe light as the engine rotates. This will give you an authentic RPM of the engine which you can compare to the electric alternator tachometer at the helm. Electric tachs come with a little rotatable selector on the back that is labeled 2 or 4 or 6 or 8. You rotate this selector switch to progressively increase/decrease the displayed RPM calculated from the pulses that the alternator puts out as it rotates. Spot on Perfect advice A faulty alternator will give your Tach wrong information. & a High Output alternator also can cause false readings, time to recalibrate the Tach as described previously
If the optical tach and the normal helm tach are close to each other then you have a different problem - probably a prop problem.
If you are getting 6 kts out of a (rather Beamy) 40 ft boat at half throttle that is pretty good. If the prop is too big you will also get black diesel smoke out of the exhaust as the engine labors to achieve full RPM's but cannot. (<-the true telltale that the engine is straining & NOT getting the air it needs) If you get to maximum book rpm's easily/quickly with the prop then the prop is too small. You would normally find a used prop shop and borrow a variety of pitches in your prop diameter/shaft diameter and test each one to see which one gives you near max speed at 3000 rpm. Hire a diver for the day & try 4-5 different pitches AFTER You determined the RPM's accurate.For the Perkins 4.108 normal max rpm's is 3,600 and maximum continuous operating rpm's is 3,000 rpms. Normal cruising is about 2200-2400 rpm's.(<-spot on, again, with a keen ear & a little practice pegging dozens of '107's & '108's they were always w/i 100 rpms of this range for the "sweet spot"...then Your sewing machine just runs, doesn't waste fuel or air & it's time for You as an owner to accept that's as fast as Your hull is going to ideally cruise) With a little experience you can hear the "sweat" zone for cruising rpm's. There is normally a definite change in tone and the feel of the boat vibration between optimum cruising rpm and the higher rpms.

OP(Hughes), this was the best posting in the thread. There IS a good chance You have a improperly set tach; There is also another issue he didn't touch on, which I must. Like the Morgan OI's, Your boat is BEAMY. Displacement hulls most all of us own, however Your's is also a full keel displacement boat with a nice fat beam. I've sailed on several Endeavour '40's (built by the same folks who made the CSY's & now Island Packets) & we could NEVER pull greater than 8-8.5kts out of those hulls shy of racing down waves. As a consolation, You have a gr8 boat, built by fantastic builders...tuning the tach & tuning the prop, then dialing in that sweet spot for cruising are all necessary; accepting the inevitable in that You're never going to preak 10kts as it's not a race boat may be something You just have to reconcile as well? Don't kill that perkins overworking it, & good luck in the quest for ideal,
-Mick