Sea Sled madness. It’s in my brain.

In this case there's no shore. The water was about 50' deep there. I live in a fjord. Just a cliff up and down. But I think your link was bang on. The poppet valve...

 

Any idea about what speed you got at 3500 rpms?

As for the swinging: have you checked if the hydraulic lines for the steering are free from air? It often takes some time for the last bubbles to find their way to the steering pump, and when they do, the oil level in the pump reservoar becomes too low. IIRC the hoses were hanging from a few points along the deckhouse side in "waves". The trick with hydraulic steerings is to have the pipes/hoses in a constant elevation towards the pump. Check bleeding situation by trying to move the engine from side to side manually; there must be no elasticity at all if correctly bled.

A bit weird with the low speed heating, could be that there is serious bottom fouling?

 

Re swinging: I only had one block of styrofoam as padding for the ram against the cliff and it crushed unevenly so the stern starting creeping to port. I corrected slightly with the outboard and it started going the other way. Like riding a unicycle. I'll saw the styrofoam in half and pad both corners and she'll be fine.

I was disappointed with the speed. At 3500rpm, only 14 knots. But that was with considerable vibration as the prop struggled on the edge of fully ventilating. And of course she's been in the water three months without anti fouling paint. The bottom is a field of barnacles and mussels and slime.

I need a very low tide, on the weekend, during daylight hours, without snow, so I can rebuild the grid. So I can clean her bottom.

Overheating wasn't as complex as I thought. I misunderstood the heating system. There's a spring loaded bypass that allows cooling water through the engine that runs in parallel with the two thermostats. My incorrect assumption was that the thermostats would handle cooling under load, while the bypass protected the engine at no to light load, but the opposite is true. Above ~2000rpm the dynamic pressure in the cooling system blows open that valve bypassing the thermostats. I'm pretty chagrined to admit getting this wrong - my understanding of dynamic pressure in a system is better than that, but I made an unfounded assumption.

 

The speed is smack on the planing hump, where the required thrust is maximum. At the same time the prop is working in the critical advance coefficient, where the stagnation point lies on the pressure side of the blade, slightly downstream from the leading edge. There is then a forward flow trying to get around the edge, which creates a low-pressure zone on the blade suction side. That is trigging BL detachement and forming of instationary cavities where bubbles collect and then are swept downstream. Result: loss of thrust and heavy vibrations. Medicine: propjob as I described to you earlier, plus bottom cleaning.

 

Heating: unfortunately the thermostats are fine. They open and close on time. Bypass valve, or Pressure Relief Valve or BRP confusingly call it, not opening until about 16-1700 rpm. It's supposed to open at ~1200 rpm.

Those thermostats are tiny little things. I'm going to leave them out for now. The engine will run cool for a bit. But cool is less harmful than overheating.

Interesting thing. Engine absolutely won't go above 1050 rpm in neutral. Shakes and complains, but that's the wall.


And now, last but not least, some interim mileage numbers. Bearing in mind I haven't taken the steps outlined by @baeckmo yet.
500 rpm 0.75 liters/hr 1.85 knots
850 rpm 1.9 liters/hr 3.25 knots
1350 rpm 3.85 l/hr 4.85 knots
1600 rpm 6.2 l/hr 5.7 knots
2500 rpm 21.6 l/hr 8 knot

Obviously these values aren't as accurate as suggested by the significant digits. But if I round up or down, even less accurate. As a comparison, the engine is supposed to consume 89 l/hr at WOT and 250hp.

 

In addition to @baeckmo excellent comments above, I think that this fouling will be a very significant factor indeed.
My brain is like a sieve for remembering things, but one bit of my Resistance & Propulsion course at college mentioned that just a layer of slime on the bottom will add at least 10% to the hull resistance.
Extrapolate this slime up to barnacles and mussels, and poor Serenity is really struggling.
A clean bum is a huge comfort for boats as well

 

Okay, so why would the engine shake in neutral and limit at 1050rpms?

A limit would make sense, but not the shake..most likely a gear position switch or cable adjustment issue.

ps, not a limit at 1050

 

Did some reading and there is a rev limiter that kicks in between 1200-1800 and takes it down to 1100, and shaking is actually normal, so disregard last.

 

DO NOT LEAVE THERMOSTATS OUT! REPEAT!! Check their opening temperature instead!

The thermostats and the pressure relief valve (which is just that, btw) together maintain the pressure required for:

• Avoiding local boiling due to hot spots in the block and cylinder head.
• Avoiding water pump impeller damage to the flexing "wings".
• Distribution of correct amount of cooling water to the parallell paths through Electronic Controller and high pressure fuel/vapour separator.

Removing thermostats has the same effect as opening the lid on the cooler of your car, there will be boiling/cavitation with cavity implosions and pitting on internal surfaces in the engine. The PRV is only sensing housing pressure, if it opens at a lower rpm than expected, either its sensor is disturbed/blocked, or the "bleeding flow" from the system is reduced for some reason, or the cooling pump is delivering more than the design flow (which is unlikely).

 

Ok, maybe a pic would help to understand, but first: those thermostats are probably lost. I think the yellow gunk should not be there; if it is vax that has leaked from the bellows, then they won't work. Again: test them in a kettle with a decent thermometer.

Then below I show a scheme of the system, the critical point of which is the branching after the block. To understand what is happening, you have to grasp the essence of the system's pump diagram. The system pressure (P) as a function of the flow (Q) follows different paths, depending on thermostats open or closed, and PRV open or closed (see "system loss...."). This pressure, after the block, should be high enough to 1/ avoid local hotspot boiling within the block, and 2/ maintain correct flow to the parallell path through fuel cooler and EMM cooler. But not so high that the pump is operating along the "flat" part of its characteristic.

Now, if you remove the thermostats with their "pressure jump", the resulting system curve (line/dotted) is drastically lowered; the PRV opens much later and the operating point (where system curve crosses the pump curve for the actual rpm) will occur at a reduced pressure. Since the typical pump curve for an impeller pump at low pressure is quite steep, there is but a small incrrease of Q. At the critical branch, this means that there will be a lower pressure difference over the FC and the EMM, leading to loss of cooling. So, unless you have inherited a filthy amount of cash and want to look at the fried remnants of a magic electronic box, I suggest that you think twice before acting.

One more to check: there should be a nozzle inserted into the outlet from the FC and EMM; probably a plastic plug threaded into the elbow. It could have been loose and later lost. That would also result in a low system pressure, and I wonder if it is the engine block temperature or the EMM temperature that causes the low speed high temp alarm.

 

@baeckmo

Very interesting drawing. I wish I could talk thru it more, just for my own knowledge.

My main curiousity is about flushing the system and how it can work with the tstat closed unless [bleed] is where that happens somehow..

In the article I read, the EMM tube can get clogged or partially clogged, which can cause a misread of actuals, but if this is so, then the system may be working, but misreading the wj temp. Rather annoying if what I read is true, but goes along with the flushing bizniz.

I plan to move to saltwater and am thinking to flush after each outing, but have no gauge of need, thus the curiousity.. And if it helps John..

 

Please note that this is unique for the E-tec; if that's not your engines, find the correct system description!

 

Gotcha.

Do these engines need/get frequent fw flushing? There are so many schools of thought on it; gets confusing..

 

Every day is an education. Often in humility. The things I didn't know that I didn't know....

 

An amazing lesson @baeckmo ! I am much in your debt. I'll just say again, if you can ever get over here, I've got rooms for you and your entourage, trails to hike, kayaks to paddle. I'll even fill the hot tub.