13mph at WOT with a packed boat??

J

jattea

New Member
Sep 5, 2008
102
Buffalo, NY
Boat Info
2003 260 Sundancer
Engines
350 Mag / Bravo III
I'm still learning my 2004 260da which I got at the beginning of the season.

Today was the first time I've had seven adults on the boat, and we probably averaged 200 lbs each... Plus a full tank of gas and more than 1/2 tank of water... so definitely a very full, very heavy boat.

I expected we would be slow moving, but I was surprised by our actual (lack of) performance. I pushed the throttle to full, and we topped out at 13 mph (gps measured). Couldn't get up on plane...

The conditions were calm, and I have the 5.7 350 mag 300hp engine.

The weird thing was the engine was topping out at 2900 rpm. I don't know much about engines, but shouldn't it have been able to achieve full engine speed? (4500rpm), despite the additional weight?

I haven't used the boat in about three weeks. And I don't know if this is an important point or not, but after my last use, I accidentally drained the batteries to zero. (I caught the problem shortly after, fixed it, and gave the batteries a full charge).

Anyone have any ideas? I'm going out again on Saturday (this time with just the wife), and I don't want to risk it if it might be an engine problem (or gas line problem..)
 
Loaded that heavy you'll need to put some of the weight forward (put 1/2 the crew in the cabin) use a little trim tabs and have some patience. 13mph seems to be the max plowing speed for our hulls, in order to increase speed you have to start coming on plane. You'll also need to make sure the drive is all the way down before starting out.

The reason the engine didn't get over 2900 rpm is because of the massive amount of traction you get on a Bravo III drive....basically the boat speed needs to catch up before the prop speed can increase further.

I don't think your issue with the batteries is related.
 
1stSeaRay said:
The reason the engine didn't get over 2900 rpm is because of the massive amount of traction you get on a Bravo III drive....basically the boat speed needs to catch up before the prop speed can increase further.
Click to expand...

That's interesting, I didn't know that. So if the prop was holding the engine back, was I wrong to push the throttle so car? Was I flooding the engine? Or straining it?
 
I don't think you were wrong to push the throttle down all the way. You're just learning your boat, that's all. :smt038 In this situation, as stated above, you'll need to use your trim tabs to lower the bow (level the boat off), because you had so much weight in the back of the boat. I don't think you have a problem at all! :thumbsup:
 
I get the same thing on my 270 with twins & Alphas so I don't think it's limited to Bravos. Part of my problem was my timing was slightly off on both engines (stupid cheap timing light...). When I'm fully loaded I send people into the cabin. It's a bit embarrassing to have to ask so I usually send the kids up first and have them sit at the V and then have the adults move up by the helm as a last resort. But everything in the cockpit and you will be limited to the 12-13 mph you experienced. These boats are stern heavy anyway - I have this:

2 - 4.3 LX Engines/Alphas (~1500lbs)
1 - 100 gallon tank (usually 1/2 - 3/4 full) (700 lbs)
1 - 20 gallon fresh water tank (full) (140 lbs)
1 - waste tank (usually empty)
3 - batteries (~150lbs)
1 - hot water heater - 7 gallons (full) (50lbs)
1- large cooler - usually full (~50lbs)
so - ~2600lbs sitting in the stern before people....

Plus people + dogs = massive weight sitting on the stern and just pushing the rear of the boat down. Play around with shifting some weight and you'll be fine. Once you are on plane then everyone can move around and get comfortable - should only take 10 seconds or so.
 
Here's the thing...
If you're engine is spec'd to turn 4500 rpm at WOT, it needs to be propped to do that under your NORMAL boating conditions.
Does it do that?

In any case, the engine was overloaded for your condition that day. Incapable of pushing the load you placed on it. Doing that often will destroy your engine. All engines, gas or diesel (especially diesel) need to be able to reach the maximum rpms stated by the manufacturer, or you need to reduce your prop pitch to allow it to do so.

Slight overloading, once in a while, is OK. But since the boat wouldn't plane, you were severely overloaded. I wouldn't run the boat like that... stay off-plane if you need to, rather than having that engine straining trying to get the hull on plane and not be able to do so.
 
Put the coolers inside and way far forward (turned sideways so they don't tip over). Ask the two, youngest, biggest, guys to sit inside in the V-Berth. Once on plane, they can move about (don't ask the fat chicks to move forward).

Your props are not holding you back. The water is holding you back. Your boat is sitting way down in the water. The props are sooo well designed for traction that they don't slip. Water is not compressible. Unless it moves out of the way, it will hold your props back from speeding up. Once the boat begins to move and come up on the water, it's easier to move more water out of the way of the props and allow them to spin faster.

If they were to slip and spin (cavitation - sucking air from surface), they would turn faster, but would be less effective. They are working perfectly as they are.
 
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tobnpr said:
Slight overloading, once in a while, is OK. But since the boat wouldn't plane, you were severely overloaded. I wouldn't run the boat like that... stay off-plane if you need to, rather than having that engine straining trying to get the hull on plane and not be able to do so.
Click to expand...


Am I still doing damage to the engine if I just keep it at low rpms / sub - 10mph?
 
You are putting a high level of torque on the engine and out drive. If you have a weak flex coupling you will find out very quickly. I wouldnt attempt to get on plane with that much weight on the boat. Keep it to a fast troll or leave some people (and fuel and water) behind. When the out drive or flex coupling fails, I doubt your heavy friends are going to kick in for the repair.
 
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So - what is the thought of having the weight distributed first and then getting the boat up on plane? You are still pushing the same weight but less water is being required to push. I know once I'm up on plane I can cruise at the same speeds I normally do and at the same RPMs. I typically cruise at about 3200rpm's which is between 27-29mph depending on water/wind conditions. When I encountered this I'd throttle back as soon as I realized I couldn't get up on plane and then moved bodies around - I don't keep it at that max plow speed until things are distributed.
 
The bottom line is- however you need to get there- weight redistribution, moving bodies around, etc.- once on plane, the engine should be able to reach towards the upper end of the maximum rpm range stated by the manufacturer. It's not rocket science...

People (myself included) by nature tend to add a bunch of crap to a boat from the day they buy it, adding weight. With a full tank of fuel and however many people, coolers and such you normally carry, max out the throttle and see if it reaches the rpm's it needs to. Do this periodically during your boating season.

I'd bet at least 1 in 4 boats are overpropped and slowly but surely killing the engines- particularly large cruisers.
You think you're getting a great "cruise" speed, but it's at a cost. Drop the pitch (yes, it'll slow you down some- but it'll save your engine).
 
Drop the drive, drop the tabs and smoothly hammer the throttle. It'll get there.
 
Kurt said:
Sounds like you had a "ton" of fun though.:grin: I limit my 240 to 4 adults and one dog for the reasons you described.
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That's about right. I have had 4 adults and 4 kids on before. There is a limit to what you can get up on plane. As others suggested, make someone (or 2) go to the front of the boat, hit the trim tabs to full down, and WOT!!!!!
:wow::wow::wow:
 
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