Can a 6BTA5.9 M1 250 HP engine be converted to a 330 HP 5.9

[randyb]

Hello All,

I have a 1995 28' TE with a 6BTA5.9 M1 250 HP engine and would like a little more speed. She seems comfortable at 2100 RPM and cruises at 18.5 knots. I'd like a little more speed. So, is it plausible, affordable and recommended to look at converting to 330 HP? I'd appreciate your thoughts, experience and insight.

Thanks!
-randyb

[loubennett]

I'm not familiar with your engine, but if you really cruise at 18.5 knots don't change anything. My 28TE cruises from 14 to 17 knots with a 315 HP Yanmar. I could probably push it to 18, but I don't like running that hard for long periods. My performance seems to be similar to what I hear from other owners with the Yanmar 315, so I think I'm getting typical performance. When I see performance like you describe, I always wonder if knots and mph are being confused. Knots are nautical miles per hour and nautical miles are about 15% longer than statute miles (the ones we use on land). Therefore, 16 knots is about 18.5 mph.

[Pitou]

I have a 1995 28' TE with a 6BTA5.9 M1 250 HP engine and would like a little more speed. She seems comfortable at 2100 RPM and cruises at 18.5 knots. I'd like a little more speed. So, is it plausible, affordable and recommended to look at converting to 330 HP?
-randyb

You've got me scratching my head on those numbers too . I have the 6BTA5.9 / 370 Turbo and push 16.5 - 18 knots at 2400 rpm depending upon fuel load (weight). Have you ever photo tached your engine for tach accuracy?

And yes I do know that engines can be juiced with fuel adjustments, adding a turbo and with modern engines, computer chip changes.. I'm not qualified to give you specifics. I'll leave that to your mechanic.

[Nancy]

Randy,

Our boat - same year and same engine as yours - gets a little over 19 knots at 2200 rpm. It's a good cruising speed.

We're getting slightly less than the rated 2600 WOT, and believe we're a little over-propped. We're going to get the prop re-worked after we haul for the winter.

[randyb]

Thanks to all for the very thorough posts. Okay I'm new and very capable of errors and misnomers. The tach and the operator might need calibration! So, I'll be more precise with the RPM and speed (thanks Nancy -- I always speak in knots! and there's no ropes just lines ) Sounds like our girl is doing just fine and thanks for the reassurances.

I'm arriving here from an oversized center console with twin overpowered gas guzzling outboards taking us over 60 knots so the comfort, the ride, the speed and the safety of the TE are all new and refreshing to us. In fact, I cannot wait to get out in the winter (we're in FL so the winter here is like spring to most of you) when the fishing is excellent.

[Old School]

Related to this topic... Does anyone have a feel for what max hull speed is on a 28TE?

[loubennett]

Hull speed is only realavent in displacement mode. It is not a meaningfull parameter for planing hulls. Just for reference, a rule of thumb is that hull speed is 1.3 times the square root of the waterline length. About 6.5 knots for a 28te. When on plane, it's a different story. A combination of form, weight, and power.

[RobS]

Jay Leonard should have some good input on the modifications to the 6B as he has/had some projects of his own going. He hasn't checked in for quite sometime, he must be in one of those Bermuda Triangles of the North.. Also a topic that will get some expert input on the BD site.

[jleonard]

You can easily and cheaply get 600 hp out of that engine...however don't expect it to last very long. The rings will pick up in the cyls and you'll be doing a rebuild.
The older 6BTA 250 engine is marginally cooled. It really is recommended to not cruise it at full power.
The experts on Boatdiesel recommend that you prop it to get at least 2700 rpm at WOT and 2800 is better, then cruise it where you are now or maybe at 2200 rpm.
Yes calibrate the tach before you do anything.
Run it "light" and you'll get 10,000 hours out of it.
Consider installing a pyrometer gage to monitor EGT (Exhaust Gas Temperature) and you'll be able to get the most out of this engine. (not sure of the specs, you can look that up online, but likely in the 900 F range)

[Old School]

Hull speed is only realavent in displacement mode. It is not a meaningfull parameter for planing hulls. Just for reference, a rule of thumb is that hull speed is 1.3 times the square root of the waterline length. About 6.5 knots for a 28te. When on plane, it's a different story. A combination of form, weight, and power.

Lou - But isn't there a point where the planing hull becomes less efficient relative to power input?

[loubennett]

Im not a hydrodynamics expert, but I think it becomes continuously higher drag as speed increases. I expect the drag curve is not linear with speed, probably more like the square of speed. Still more power, more speed assuming you adjust the prop to get the extra power into the water. At some point you likely run into stability issues and the boat would be pretty scary to drive.

[RobS]

When on plane a planing hull efficiency increases with speed as the boat lifts and trims out. Then there is less bottom contacting the water so frictional drag decreases too. BUT then there is the efficiency loss of the running gear as speed increases, mostly with inboards. And then the power/fuel curves of the specific power plants. Etc, etc. So yes, Old School, you are correct.

[loubennett]

This is a complex subject. There are many forces operating on the hull with different ones dominating in different speed regimes. The best short explanation of the combined effects I could find is a Wikipedia article.

http://en.wikipedia.org/wiki/Wave-making_resistance

Please examine the graph in the planing hull section that plots resistance to weight ratio versus speed to length ratio. There are three distinct regions for a planing hull - displacement, semi-planing, and planing. Please remember the speed to length ratio is the speed in knots divided by the square root of the waterline length. When this is about 1.34 that is the displacement hull speed. The region where the planing and semi-displacement hulls are the same is the speed region where a planing hull is climbing out of the hole. The region where curve becomes less steep is where the planing hull is on plane. Drag still increases with speed, just not as fast. The resistance curve in the planing region is also not linear, it curves upward. The bottom line is that all the comments are correct, but they address different parts of the curve. If we define efficiency as the ratio of speed to resistance you will see that in the initial portion of the planing region, efficiency does increase with speed. However, as speed further increases, efficiency reduces and eventually becomes lower than at the onset of planing. Please remember this curve is for a notional hull and will vary depending on specific hull design, but the concept is valid. Also, I expect the curves ignore the drag of underwater appendages (skeg, rudder, struts, etc. ) which in the case of the 28te contribute significant amounts of drag, especially at higher speeds.