Speed

Salty Pete · 29 December 2023, 05:55

I have a Highfield 380 and uses very little fuel. One of its attributes is, it goes on the plane very quickly, which is also a problem.

On our inland waterways we have speed limits mainly 5 or 8 Knots.
5 Knots is OK but I cannot travel at 8 KNots because around 6 - 7 Knots it goes on the plane and shoots up to 15 Knots.

What is the best way to slow the boat down? Adding weight or changing the prop although I can't see that doing anything. Take my Mother inlaw boating and drag her behind the boat. (PS I'm not married in case this upsets your timid little feelings)

Thanks if you can help.

paintman · 29 December 2023, 12:12

You'll likely find no shortage of men offering their MIL!

Adjusting the engine trim or redistributing the load in the boat would be the first things to try.

Fenlander · 29 December 2023, 15:11

Use a small second/aux OB for river use??

Steve509926 · 29 December 2023, 16:06

Maybe I'm being a bit thick and missing something! Why can't you throttle back once it's on the plane and just keep at 8 knots.
My SIB gets on the plane around 7 - 8 knots and shoots forward, but once on the plane I can throttle back to 7-8 knots and keep it there.

ShinyShoe · 29 December 2023, 17:42

Or...

Go at 5.9 knots...?

I tend to find my car shoots off to 85mph if I put my right foot down. But I've discovered if you lean a bit lighter you can stay under the speed limit which seems to mean I gather less points these days...

Salty Pete · 30 December 2023, 01:25

Paintman: When I am the only one in the boat there is nothing to distribute. Adding weight to the boat would obviously work but when the river becomes unrestricted that is going to increase the fuel expenses.

Fenlander: There is no room on the transome for another OB.

Steve509926: That would seem obvious, but it doesn't work. I go on the plane at 6 knots and when I throttle back it goes off the plane and goes back to 6 knots.

Shiny Shoes: Thanks mate. I use cruise control when I'm driving, assures I stay at the speed limit. My boat doesn't have it.

I am beginning to consider that dragging something behind my boat to keep it off plane may be the answer and I can haul it in when the speed is unrestricted.

Why am I conserned about a fwe knots of speed. My boat is only 3.8 metres and with boats overtaking all the time it makes for a rough ride.

Peter_C · 30 December 2023, 01:43

Is it a no wake thing or a speed thing? The faster you go the less wake your little boat will produce. Interesting as in the USA our "NO WAKE" speed limits are typically 5mph or 3.5kts. Anything more and bigger boats start producing LARGE wakes.

Trim the outboard up a little and it won't jump onto plane, but it will throw a bigger wake as it plows the water more with the bow up.

Max... · 30 December 2023, 08:57

I'd just pop a teeny noddy boat prop on it.

Salty Pete · 30 December 2023, 10:03

[QUOTE=Peter_C;870548]Is it a no wake thing or a speed thing?

Neither, it's stupidity. There is a 5 Knot speed limit on a large area of water and during a storm the waves are bigger than probably any boat that
uses it could make. I was travelling at 5 knots and the Police Boat overtook me doing about 30 Knots so if it is an environmental thing the Police Boat's stuffed that.

tinker · 31 December 2023, 09:49

You could try an outboard hydrofoil and see if you can lower the speed you go onto the plane.

Steve509926 · 31 December 2023, 11:55

From your description it sounds like you are saying you have "2" speeds, < 6 kts or > 15 kts, and nothing in between?
I don't know your set up, remotes or tiller, but if that is the case I'd be looking at your throttle settings, linkages etc as it sounds like it's a very sensitive to adjustment. IMO you should be able to maintain a speed in between 6 - 15.

Salty Pete · 01 January 2024, 01:18

Quote:

Originally Posted by Steve509926

From your description it sounds like you are saying you have "2" speeds, < 6 kts or > 15 kts, and nothing in between?
I don't know your set up, remotes or tiller, but if that is the case I'd be looking at your throttle settings, linkages etc as it sounds like it's a very sensitive to adjustment. IMO you should be able to maintain a speed in between 6 - 15.

Good call Steve. So it could be slack in the throttle cable/linkages alowing the engine throttle to move itself.

I'm out to the shed now but, by the time I've finished probably nothing will work.

I'll let you know how I get on.

Thanks again.

Fenlander · 01 January 2024, 02:49

Is this motor on remotes and is it the efi version?

ShinyShoe · 01 January 2024, 20:34

Quote:

Originally Posted by Salty Pete

.
Shiny Shoes: Thanks mate. I use cruise control when I'm driving, assures I stay at the speed limit. My boat doesn't have it.
.

I'm not sure you should need cruise control on a boat! You don't have hills to go up and down. So the only things affecting your speed once the throttle is set should be the wind and tide/current. You'd feel it try to plane at 6.1knts presumably and easy off the throttle.

Unlike on the roads there isn't generally a guy with a radar gun out to get you. Some harbour masters do have a radar gun but I very much doubt you are getting a fine for doing 6.1kts. if you can't spot you are about to plane and end up at 15kts... That's a different story.

ShinyShoe · 01 January 2024, 20:38

[QUOTE=Salty Pete;870550]

Quote:

Originally Posted by Peter_C

Is it a no wake thing or a speed thing?

Neither, it's stupidity. There is a 5 Knot speed limit on a large area of water and during a storm the waves are bigger than probably any boat that
uses it could make. I was travelling at 5 knots and the Police Boat overtook me doing about 30 Knots so if it is an environmental thing the Police Boat's stuffed that.

I don't think it is stupidity. I don't know the area of water you are referring to. But I used to launch sailing dinghies in a harbour with a speed limit. If something went past that was (or thought they were exempt) I could go from holding a boat in knee deep water to partially covering a buoyancy aid enough to lift my feet off the ground. The ALB was particularly prone to it. So were jet skis.

You are right the same wash may be caused by a strong sea state. But I'd not be in the water with 8year olds trying to launch dinghies if it's blowing F7...

ShinyShoe · 01 January 2024, 20:39

Quote:

Originally Posted by Max...

I'd just pop a teeny noddy boat prop on it.

Think he wants to be able to disable tortoise mode when he has left the harbour area. Changing prop seems an extreme aproach

Max... · 02 January 2024, 08:51

Quote:

Originally Posted by ShinyShoe

Think he wants to be able to disable tortoise mode when he has left the harbour area. Changing prop seems an extreme aproach

Well, the OP mentioned use purely in inland waterways not harbours so I assumed this was a major use for his boat. Seeing as changing a prop takes about 1-2 mins I thought it was something less than 'extreme'.

Salty Pete · 03 January 2024, 11:46

Quote:

Originally Posted by ShinyShoe

Think he wants to be able to disable tortoise mode when he has left the harbour area. Changing prop seems an extreme aproach

I can carry my dive gear with me and jump out the stern and change props in accordance with the speed limit.

Yeah Shiny Shoes I see your point. The passage is quite narrow although it is a wide body of water. When you are only going 5 and someone wants to pass at 15 it gets very rough.

Fenlander: It is a remote throttle with EFI if that means "fuel injection."

Steve: I have checked the throttle linkages all good I can't move them, there is no slack.

I may have a chat to the dealer.

Thanks everyone

Fenlander · 03 January 2024, 13:01

I asked re remotes/efi as I owned the similar lean burn tech Suzuki 20hp efi in 2016 and made this comment when I reported on it...

"The "lean burn" ECU controlled mixture operates by giving loads of fuel to accelerate then leaning off as much as possible while maintaining revs for any given throttle opening. In some tests they've commented you can feel this happening and there is an impression having levelled off the throttle that you might be about to slow down so you give it a bit more where it responds with gusto then you have to back off again. I'm being super critical here... not an issue... but after the gutsy through the range 2-stroke it just feels less linear in its power delivery."

And having put many more hours on it after writing that I did come to the conclusion in certain circumstances the throttle response was really quite non-linear. I could only imagine that effect being a greater when used with remotes and wonder if by chance your outfit characteristic is coinciding with this behaviour of the outboard to give the result you have?

chipko · 03 January 2024, 16:40

Must admit struggling to see any real problem here.

All planing craft have that ‘no go’ zone where you’re exceeding the hulls max displacement speed but not reaching minimum planing speeds with the bow pointing skywards until it climbs out of the hole. It’s not a pleasant ride, and it’s wasting fuel but there is no reason why you can’t hold speed in that zone with the throttle if you really need to.

I suppose you could trim motor out to help the hull not climb out of the hole which might give a knot or so more speed. You could also try deploying a drogue, or even a bucket, adding resistance which may keep you longer in the no go zone. You’ll be pointing skywards and using shit loads of fuel though.

Surely better just to stick at the hulls max displacement speed of 5/6knots, saving fuel and wash, until you’re clear of the restricted zone.