New bottom job - props tuned new numbers

[DaveK]

I finally had the opportunity to take the boat out after the completion of the bottom job and the props being tuned. Prior to this work it would take 1500 RPMs to get to and maintain 7.0 - 7.5 kts and WOT would produce approximately 17 kts.

This past Saturday went out for a short day cruise, the first leg was 3.8 nautical miles with the wind blowing about 90 to 110 deg off the starboard side. The second leg was 3 nautical miles into the wind, and the final leg was approximately 6.5 nautical miles with the wind off the port quarter.

On the first leg I was able to maintain 7.5 - 8.0 kts at 1300 RPMs. The second leg into the wind the speed dropped only slightly (I suspect a lift from the current) to 7.0 - 7.5 kts at 1300 RPMs. The third leg with the wind quartering from behind I was able to maintain 7.5 - 8.0 kts at 1200 RPMs.

I only tested WOT on the third leg but did see an increase in speed to 18.3 kts with very short up ticks to 18.5 kts.

I am very pleased with these numbers and hope that the reduced RPMs at hull speed will relate into measurable fuel savings. That would be a nice bonus. We are planning a three day trip of approximately 180 nautical miles in May so I hope to average fuel usage over that trip. I will very pleased to see a total of 5 GPH or less.

One other change, the starboard engine made 2800 RPM on the nose which is max rated RPM. The port made 2750, until I can measure off the crankshaft to verify the tach is accurate, is that enough of a drop to be concerned? I run at hull speed most of the time with an increase to 2100-2300 RPMs for 5-10 minutes or so for about every four hours of running.

 

[Tim Powell]

I bet that was good to you like a new WIFE as freebird would say. They are grate numbers...

 

[Summerfun]

Did you drip the bottom paint and start new or did you just paint it. I have been debating on stripping my bottom that has 30 years of bottom paint I have gotten mixed reviews if it worth it.

 

[motoryacht lover]

I had the bottom sand blasted and I did not see any measurable or noticeable increase in performance. My boat is a 54 Viking with a top speed of 30 knots. That is everything perfect fresh out of the Travelift.

 

[Boatsb]

I've seen a 2 knot increase in a few when done right. If there's a 1/4 inch of paint built up and rough it will slow you down.

 

[jim rosenthal]

I think you should strip the bottom. Either mild chemical stripper, or soda blasting.

 

[Walter P]

It's probably a good idea to strip the bottom but it's a bear of a job. The best way I think is to hire an outfit that specializes in that nasty job. They make it look easy and the results are usually very good. I have no idea what a job like that would cost ($) but whatever it is, it's probably worth every penny. Years ago when I had more time and less money I used to do most of my own work and I can tell you from experience that sanding years of old bottom paint has got to be the worse job to do on a boat. Good luck and have fun whatever you decide......

Opps...just re-read your post and you did have your bottom done....was it stripped or just repainted?


Walt

 

[Boatsb]

Most places will not let you sand off all that paint. It's an environmental problem and must be contained.

 

[DaveK]

Did you drip the bottom paint and start new or did you just paint it. I have been debating on stripping my bottom that has 30 years of bottom paint I have gotten mixed reviews if it worth it.

I did not strip the paint as this was the first time I've had the bottom painted and wanted to make sure it had good functioning paint. That said...if I had the time and were prepared for the cost I would definitely recommend it. I will start planning and preparing now to have the bottom stripped as part of the next bottom job.

I believe most of the current improvements in performance came as a result of the prop work.

 

[DaveK]

It's probably a good idea to strip the bottom but it's a bear of a job. The best way I think is to hire an outfit that specializes in that nasty job. They make it look easy and the results are usually very good. I have no idea what a job like that would cost ($) but whatever it is, it's probably worth every penny. Years ago when I had more time and less money I used to do most of my own work and I can tell you from experience that sanding years of old bottom paint has got to be the worse job to do on a boat. Good luck and have fun whatever you decide......

Opps...just re-read your post and you did have your bottom done....was it stripped or just repainted?


Walt

Walt,

Just repainted this time....and you are correct about sanding bottom paint. The last time I personally sanded and repainted the bottom of a boat was almost twenty years ago! I said then it will be the last time I do that, fortunately so far it has been the last time.