Prop size???

seanf3f3 · Post by **seanf3f3** » Sun Aug 19, 2007 4:01 pm

The gear ratio is 1.91:1. Having trouble getting over 3000RPM's. The props are 18X21. Is there anything else that would help with this issue? The engines have been rebuilt and still experiencing the same problem.

schultz · Post by **schultz** » Sun Aug 19, 2007 4:21 pm

If you are only turning about 3000 RPM WOT what speed are you getting?

seanf3f3 · Post by **seanf3f3** » Sun Aug 19, 2007 4:33 pm

18 knots

franklyprice · Post by **franklyprice** » Sun Aug 19, 2007 4:51 pm

That's about the right speed for that RPM so I would be looking at things that either rob power or create drag. Things like, air supply to the engines, fuel supply to the engines, are you getting full throttle? How's the bottom look? You seem to either have a power issue or a drag issue. Also, if you have one engine that is not running correctly you could be dragging the other one down along with it, so if it were my boat I'd be making sure both engines are sound and in good tune and as above mentioned, getting full throttle, then or at the same time consider drag, both on the props and the bottom as a whole. Have you run with the hatches open, to see if it's an air flow problem?

seanf3f3 · Post by **seanf3f3** » Sun Aug 19, 2007 5:07 pm

I have had this problem since I bought the boat last year. Rebuilt engines, tranny's and carbs. Had prop'secut at H&H. Bottom is clean. Running out of ideas. Thanks for the advise.

lobsta1 · Post by **lobsta1** » Sun Aug 19, 2007 6:55 pm

Have the same gears & have my props cut back to 21 x 18. Original 1978 spec on a stripped B33 FBC was 21 x 20 with a WOT of 4000 on the 1978 454s. How old are the spark plug wires. On the older Mercs 3 years was the max on the wires. After that they would break down under load. You could also have a blocked screen on the fuel pickup. Can you temporarily rig a couple of 6 gal. cans & try for one run to a higher RPM? I believe you either rebuilt or repowered. Are you sure about the timing & getting proper advance? Depending on engine, I believe it should be 8*BTDC with an advance of 24* at 3000 RPM. If you have an advance timing light check if you have 32 degrees total advance at the 3000 RPM. Sorry if I am just going over the things you have already tried, but that's just the things I can think of off the top of my head. Good Luck Al

seanf3f3 · Post by **seanf3f3** » Mon Aug 20, 2007 6:45 am

I will try a side tank. Willing to try anything at this point. I'll let you know. At this point I would rather be working than fishing!

seanf3f3 · Post by **seanf3f3** » Mon Aug 20, 2007 6:54 am

Al, what are you turning for RPM's and getting for speed with the 21X18's?

Post by **dougl33** » Mon Aug 20, 2007 6:57 am

Sean, Somethings not right with either your engines or your trans. With a diameter of only 18 inches you should be getting way more rpms. Before re-powering with diesels, I had both 20dx18p 3 blades and 20dx16p 4 blades on my 1.91:1 trans. Both sets allowed me to easily spin 4K plus rpms. How's the gennie working? Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA [img]http://www.bertram33.com/photogallery/p ... sabeth.jpg[/img]

schultz · Post by **schultz** » Tue Aug 21, 2007 3:48 am

Sean, Lots of good advice already. Even though the engines have been rebuilt I would take the time to do a compression check on both of them. The next time you haul the boat if it is with a travel lift I would ask the operator to give you a weight check. Cliff Schultz 1983 33' SF "Final Approach"

retman · Post by **retman** » Tue Aug 21, 2007 4:38 am

As to the weight check. When I had Retriever (ex Rebecca Rose) surveyed. The operator of the travel lift stated she was around 17,000+ pounds. This was with 1/2 water and 75 gallons short of full fuel. Otherwise completely empty. I'm a little suspect of his scales accuracy based on the spec's given for this boat. Bill Arnold

photo finish · Post by **photo finish** » Tue Aug 21, 2007 6:20 am

Everytime i am on a lift they tell me the scale is broken.

lobsta1 · Post by **lobsta1** » Tue Aug 21, 2007 6:34 am

Sean, At 3100 I will running between 17 > 18.5 kts. WOT is 3950 at about 24 kts. Al

Sean B · Post by **Sean B** » Tue Aug 21, 2007 8:22 am

quote:Originally posted by retman As to the weight check. When I had Retriever (ex Rebecca Rose) surveyed. The operator of the travel lift stated she was around 17,000+ pounds. That can't be, should be in the neighborhood of 23,000 pounds Sean Burlingham "Island Time" 1987 Bertram 33 SF Melbourne, FL SBurlingham@cfl.rr.com [img]http://www.bertram33.com/photogallery/p ... d_Time.jpg[/img]

Post by **dougl33** » Tue Aug 21, 2007 8:30 am

Those travel lift scales are never right. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA [img]http://www.bertram33.com/photogallery/p ... sabeth.jpg[/img]