2001 Bertram 510

RCRAPPS,

You are right on your numbers. I run the engines slightly above planing speed as thois is the most economical - Spain's diesel is now about $7.50(US)/gallon. I will do between 30 and 32 knots WOT depending on sea/bottom. There are many Bertram 50's with the same engines so mine can be considered slightly overpowered. I cut 1" off my props when I brought the boat from the US as the water in the Med is denser with higher salinity and could not reach 2300 RPM - I am a firm believer in being slightly underpropped to avoid problems. I had a hose break doing 31 knots while cleaning turbos after a long trolling day and no problem after a very short overheat - and that was 700 hours ago. My mechanic says these engines will outlast me!!!!

Rolando

Started 31X39 and cut 1" pitch. I believe its important to be slightly overpropped and not have the engines overloaded. You hear many people say you must need an overhaul when you reach 2,000 hours but that happens when your engines are just too small for the boat and you push them hard. Like the old B46's with DD71's.

Yea, the Med is very salty! There is a net inflowing current fromthe Atlantic because of evaporation and not enough reiver flow.

Rolando

I am not sure I am following the process.

If the seawater in the Med is denser (saltier) than standard seawater, your vessel would actually displace less volume (it would be more bouyant) and therefore you should require additional pitch, not less? Your vessels' waterline should be sitting slightly higher than in standard seawater (1.025 kg/m^3 or about 64.4 lbs/ft^3) and you would realize a reduction in wetted surface and therefore resistance? Wouldn't this be enough to overcome any friction effects on the propeller blades?

It is common to reduce pitch when you are taking a vessel from the ocean to the Great Lakes, because you are actually displacing a bit more volume in the lower density (specific gravity) of fresh water and your waterline is slightly deeper than before.

I must admit though I have never propped a boat in the Med before.

Tried now to google to find the place where the mentioned the implications of moving from the Atlantic to the Med but could not find it. I remembering reading about a UK boatbuilder and their specifications on propellers by intended boating locations. I am not sure where the effect nets out as I did not notice a waterline difference when I shipped my boat from Florida to Europe. What I did notice was that I lost almost 100 RPM. In my case I decided, after much reading, to reduce pitch by 1" and that did it. I "guess" the reason might be complex and might also be influenced by somewhat less waterline contact but more frictional forces and a harder working prop moving through a densed medium. Again, in MY case the same boat with the same weight lost 100 RPM and almost 2 knots when I took the boat off of the carrier ship. I now have lost the 2 knots, which for me is trivial, but the engines are working with far more headroom. Hope this helps. I'll continue looking to see if I find the articles.

Rolando

I don't know the specifics of the water. BUT, I ran a brand new Arneson boat that was built in the med. The owner seatrialed the boat in the med while they were trying different props. The engines made RPM's and everything else. The boat was shipped here to South Florida and the engines were SERIOUSLY overpropped. We were seeing over 90% load at 1800rpms. Maybe the specific gravity of the water has something to do with it. That's just my limited experience.

Its probably a difficult subject to analyse. I have read some more today and hear both that it should be faster or slower and some say either answer from their own experiences. I can only talk about my own experience with my boat and try and make some sense from it. I have also read that its not just density, but also the effects of water temperature on drag (Med is always colder than south Florida) and hull shape/type deep vee vs fast planing hull. Just don't know if there is one clear answer that applies to all boats. When people talk about fresh vs salt water some also indicate that fresh water lakes are usually at some altiude vs sea level and engines lose some power as altitude increases.

Rolando

I agree there is not an easy answer, still scratching my head on this one.

One other thing to look at would be fuel quality - does it differ in the Med (from Florida) and is there a chance that it has a lower Cetane rating? This may contribute to a decrease in power.

I don't think the fuel could differ that much.....We lost 200 rpms. This was a new boat with the new Man 800's. Salinity content possibly and the water has more coefficient of drag? Air temperature, was about 20F difference, but not sure that is enough either.....Fuel load/weight didn't make any difference either, whether we had 200 gallons or 800 gallons on board.....

WELL, diesel costs a lot more in Europe, so it must be better!!!

Other than the price I don't know the difference between the European blends of marine diesel versus the US blends.....

A couple of perceptions: fuel is more expensive but I do feel its better quality. You don't ever hear people doing all the crazy things they do with magnets or fuel recirculation, and they DON'T add grains like in the US. In fact, our lowest grade gasoline octane is 95!

I just read where all the differences are supposedly very small - like 2%. My correction was quite small 1" - pitch from 39" to 38", 2.5%. It's just that this got me 100 RPM.

Rolando

From Wiki....

In the past, diesel fuel contained higher quantities of sulfur. European emission standards and preferential taxation have forced oil refineries to dramatically reduce the level of sulfur in diesel fuels. In the United States, more stringent emission standards have been adopted with the transition to ULSD starting in 2006, and becoming mandatory on June 1, 2010 (see also diesel exhaust). U.S. diesel fuel typically also has a lower cetane number (a measure of ignition quality) than European diesel, resulting in worse cold weather performance and some increase in emissions.

Diesel fuel - Wikipedia, the free encyclopedia

A lot of the published data on diesel fuel comes from an on-highway perspective. I have seen variability on product delivered to the marine markets, can sometimes be a 'dumping' ground for the unscrupulous.

Not saying it is the same in EU, but it could be one of the incremental factors adding to the 1" pitch change. Did your prop shop perform the work to Class I standards and provide you a scanned readout of the new blade geometry?

In Spain there is no fifferentiation between marine recreational and highway. There is a difference in others, at least UK, where they put pigments for police to verify as there is a substantial price difference. In Spain they have different fuels for the commercial marine, agricultural and home use and the fines if they catch you using it are extremely high.

As far as my pitch reduction, I did not go to a prop-scan place as there was only one in Spain and in the other end of the country. As this was done almost 9 years ago I don't remember many details. They were checked for symetry and corrected?? Here its not like south Floroda orthe Caribbean - no coral reefs and very few hazardous places. Most prop damage usually from hitting some debris of running after storms.

Just a note, right after doing the pitch reduction I also has the bottom scraped for removing all those year's layers of anti-fowling. Its possible some of the extra 100 RPM also helped by this but its been a long time. Now I am not sure if both measure did a bit more than 100RPM. I wanted to reach 2375-2400RPM for the rated 2300. I also read a lot at boatdiesel.com and you can find a lot of experience on the subject and how important it is to have some headroom.

Rolando

Yes, you can pick up both speed and rpm's by peeling a dozen layers of old bottom paint off. Just look at how much a gallon of bottom paint weighs. We did a 45' Searay and peeled about 11 layers of hard paint off a while back. Put seaslide on the bottom after 2 coats of paint. The boat picked up over 100 rpms and 3.5 knots by doing this.

Are you sure it was just paint. 3.5 knots seems a lot to me. Was other work being carried out at the same time. New injectors to engine, prop being in bad fouling and so many other things.
100 rpm if the bottom is a bit fouled makes sense though, but if this is clean and it is just extra layers of paint it should still not happen.

3.5 knots from just paint removing is impossible in my book!

It did happen. Bottom was cleaned before the intial seatrial, as there was a seatrial/survey which included hauling the boat. 11 layers of bottom paint is a lot of weight and there were many area's where an 1/8" thick piece 6x6" peeled off and they just painted over it.....So I'm sure that created some drag. We did apply sea-slide over the bottom paint. Props were un-changed, the boat also picked up the same in speed at the same 1950 rpms. Nothing was done to the engines except oil changes/fuel filters etc...... Hard parts on engines were all the same- turbo's, injectors, etc etc......

I was told the same story on a 70' Azimut and he saw the same results......he also had many many layers of bottom paint. There is a lot of weight per gallon of bottom paint, even if you let the liquids evaporate in it......So you figure 3 gallons a coat x 11 coats= 33 gallons.....over the years......

The weight of bottom paint is insignificant, even for 33 gallons, and consider that you lose some "can weight" to evaporation as the paint cures. Even at 50 lbs. a gallon, 1650 lbs. is not enough to cause the issue. Hell, some people carry more beer/liquor than that on their 70 footer!

BUT, the surface roughness which translates to skin friction as a result of bottom paint build-up is significant, and this would most likely be the culprit in this case.

It depends on the boat. On boats that barely stay on plane when they're new due to how much power they have or hull design, it can make a big difference if they're right on the tipping point. 1650lbs is pretty significant on a 45' planing hull, a drop in the bucket on a 70'. But the texture issues and possible slight change of shape on the bottom. I know the difference between 2 coats of bottom paint and none at all are usually around 2 knots......Most of the time when they have that many layers of bottom paint on, they have many area's where palm shaped chips have come off and there is a 1/16" or 1/8" ridge between a coat or two where the chips came off and all the other layers that didn't fall off......

The 58' Azimut I run, will cruise at 26 knots with full fuel, or if we're loaded down with 2000lbs of soda's,beer, and other stuff in the lazzarette for a 2 week trip in the Bahamas, it will only cruise at 24.5 knots until you burn around 250 gallons of fuel off and then it picks right back up to 26 knots......