Docking I/O vs. IB

[JV II]

Today, we had a cross current to the slip going port to starboard. There was a 20 mph wind pushing into the slip. It was a challenging situation that would have made me nervous with my other boat (no bow thruster). The problem is that the light bow would swing to starboard from the current and then get caught by the headwind, rotating you faster to starboard.

I docked my boat with no problem, no stress, no contact, and no help. I completed my rotation as if to back into the slip to port of mine. As I drifted to starboard, I turned the wheel full to port, put the port throttle in reverse and worked the thruster. I actually backed up and to moved against the current to port perfectly parallel to the finger and within one foot of it.

Minutes later, a twin IB with no bow thruster put on a nice show of bumper boats. Mistake number one, no knowledge of the cross current. Mistake number two, not anticipating the wind. Before he could start the rotation, the wind pushed him into the bow anchor of the boat to starboard of his slip. He backed up and made a second attempt. Same mistake twice, except he reversed, and left the helm in a panic scurrying up the side deck to push away the boat he was drifting into again. Mistake number three, leaving the helm while his boat was in reverse. Luckily, he quickly realized he was on a runaway boat and got back to the helm before colliding with another boat (almost mine). On attempt number three, he was able to get the last 2 inches of his stern in the slip, but could not control the bow as the current took it to starboard and then the wind caught it and pulled him out of the slip and back broadside against the bow anchor of the boat to starboard of his slip. With a lot of help on the dock. he was able to get it in using the lines.

No doubt, he made some rookie mistakes. A bow thruster would have made it much better, but I'm not sure that the rotation of his props would have helped keep his stern upcurrent.

In my analysis, a twin stern drive with a bow thruster is the ideal set-up for this common situation. You can vector the thrust of the stern drives to push your stern to port or starboard and use the thruster to control the bow. I can actually walk the boat sideways.

With an IB, I think you can kick the stern to either port or starboard, depending on which throttle you use. Maybe some IB boaters can comment on that. If so, an IB boat with a bow thruster should be able to walk sideways by using short bursts of alternating forward and reverse on opposite throttles and the bow thruster.

 

[chumbley]

Inexperience knows no boundaries. Adding something else to think about in an already tense situation may not be helpful. A poor captain can screw up with any amount of technology, and they can do it in any conditions. We've all seen it happen, I'm sure.

There is no doubt (in my mind anyway) that bow thrusters help, and would be very handy to have. I just don't know how much thrusters can offset a lack of skill, and at what point having something else to mess with just makes it worse.

 

[sbw1]

In my view there is no substitute for big props, big rudders and a good keel. No thruster is needed if you know what you're doing.

 

[trit21]

No thruster is needed if you know what you're doing.

Amen !

 

[tbirdvet]

I noticed I also have great success with my bow thruster. I can offset the bow movement due to the cross wind and keep it straight as I work the throttles. Perhaps with more practice I will be able to do without the thruster but I'm glad I have it just in case!

 

[rcknecht]

Anything under 1,000 ft no bow thruster is needed... But they sure can make you look good... My neighbor has bow and stern thrusters on his 341 Meridian and he never has a problem docking... I can't wait until the barnacles and salt water to eat up those thrusters so I can have my fun watching him docking...

 

[Sua Sponte]

I have a 500 Dancer with no thruster and big Cat diesels.

The biggest difference I have noticed is the huge difference between the docking-speed torque of my boat and other larger boats that have gas engines.

I mean if you throw my boat in gear, you're going seven knots. The only thing you can do to go any slower than that is to hit the electrnic engine RPM supressor to drop the idle RPM to a bone-jarring 500 RPMs....or pop it in and out of gear to not violate no-wake zones. I was totally unprepared for the amount of torque at idle, which really helps with docking.

Reading a story like this makes me really want a thruster....or at a minimum, convince myself that I need one.

 

[AKBASSKING]

Having IB I have done a little practice with on enigine in reverse while the other fwd. A captain friend of mine showed me how it was done with RPMs.

I still don't quite understand it and will spend many hours in open water to practice as my last ordeal at the dock almost gave me a heart attack................

Someone want to put the procedure in plain english so i can understand how it works? :smt038

 

[JV II]

8 responses and still no answer to my question: "With an IB, I think you can kick the stern to either port or starboard, depending on which throttle you use. Maybe some IB boaters can comment on that. If so, an IB boat with a bow thruster should be able to walk sideways by using short bursts of alternating forward and reverse on opposite throttles and the bow thruster."

I don't need to hear of boasting about docking skills or which is better, IB or SD. Tell me what your boat can do if you have an IB. Can you swing that stern sideways using your props? With a bow thruster and the props, can you hold your position against the wind or current? The cross current/wind scenario I mentioned is common.

 

[Sua Sponte]

Tell me what your boat can do if you have an IB. Can you swing that stern sideways using your props?

A little; not much. When you first throw one engine in gear, it walks a touch....maye a foot or two, until the props start pushing enough water to do what they are designed to do.

So, if the stern is close, you can nudge it...but you do not have the purely lateral thrust of a thruster that is devoid of fore/aft push.

Does that help?

 

[LTD.330]

Yes, absolutely, with a twin screw inboard you can kick the stern to the port or starboard. Realize that when you are pushing one end of the boat one way, the opposite end has a tendency to move in the other direction.

Now, just how much force the boat can overcome while doing this is dependent on several factors. Rudder size, prop pitch, prop tunnels v. deep V, distance between screws, mass of the boat, etc. All play a factor.

 

[JV II]

that helps. I docked a 36BD stern in and recall the stern walked about 2 feet to starboard when I put one of the throttles in forward (ETS). I can't recall which one that was, but with counter rotating props, I imagine that the stern would kick to port if I only engaged the other throttle. I understand the physics of how it happens, but don't know if the effect can be used to control the cross current situation with the help of a bow thruster.

 

[Mike Gazdik]

Since I am a newbee to twin inboards I will chime in. I am still learning. I bought this boat late last season so I only had a handful of docking experiences. My first time out this year, upon return was ugly. I dock in a river and the river was flowing from West to East, and I had about a 15mph crosswind from the West. My floating dock is on the South side of the river, so I dock from North to South. I noted when leaving that the bow quickly was blown to the port side as I backed out and knew my return would be challenging.

My docking was ugly, I didn't hit anything, but I messed around in the middle of the river for 3 or 4 minutes trying to get the bow turned into the wind. I used power on the port side to eventually swing the bow to head due West. After I finally got that under control I was able to slip right into my dock. I was amazed at the power of the river and wind to defeat my attempt to turn my bow.

Twin inboards are awesome, but they do not make up for a lack of experience. I was humbled. I cannot compare to twin I/O's because the only experience I have is single I/Os. I don't know how the heck I would have docked with a single.

 

[ziekman@cox.net]

I've got IB's with 8.1 horizons. No bow thruster. Yes, with the steering centered, you can move the stern to port or starboard with the props. If you want to move your stern to port, but not move forward or backwards, you engage the port engine forward, while at the same time, enage the starboard engine forward.

I was always under the impression never to use the steering/rudder, but I like the suggestion above, and will give it a shot.

 

[ziekman@cox.net]

YES, I DID MEAN REVERSE!!!!! Thanks for catching that!

 

[wkearney99]

Yeah, in theory you can use the rudder behind the engine in forward to counter the pivoting action. That is when the rudders are neutral (just straight forward) then one engine in reverse and the other in forward will pivot the boat. The theory is if you turn the rudders hard over, the thrust from the forward engine against the rudder will counteract the rotation behind pushed by the other engine. Remembering that the relatively small rudder in a powerboat only has use if there's water being pushed against it. But in reality the minute amount of adjustments necessary to do this, when juggling everything else like current, wind, nearby obstacles, passengers and spectators, makes it next to impossible to do it reliably every time.

Systems that tie it together with GPS (IPS, Zeus, etc) allow the computer to do it. Of course that opens up a whole range of rants about computer controls. Much like the claim about those with bow thrusters being overly dependent on them.

So beyond all the tricks and theories it's still necessary to get a feel for how your boat responds and use that to plan several steps ahead for the conditions presented. Understand what you can get the boat to do and what the wind and current will do. The bit of drift or spin they cause can often be used to your advantage. Like being able to drift up to a piling and then pivot around against it. Better to have controlled contact on the rub rails than a bill for repairs.

 

[ziekman@cox.net]

SFERGSON - by your statement: You have to turn the rudder hard over away from the pier, place the pier side engine in reverse, the other in forward and manage the power to keep the boat from moving forward or backward....

do you mean that if the dock I want to tie up to is on my port side, then I can move the boat sideways towards it by turning my steering wheel to starboard hard, then put port engine in reverse, and starboard engine in forward?

 

[Sua Sponte]

Actually that's not quite true.

A inboard twin engine boat can in fact power sideways. You have to turn the rudder hard over away from the pier, place the pier side engine in reverse, the other in forward and manage the power to keep the boat from moving forward or backward.

It's not easy, but it can be done.

Individual experiences/setups may vary.

My rudders are vitually useless unless turning a wake.

With both engines engaged, we have almost 1,400 HP spinning props at idle engine speed of ~750 RPM. If it is in gear, the boat either goes 7 knots or spins like a top. No amount of rudder application while not moving is going to counter the spin effect to any measurable degree, let alone arrest it..

I would wager that gas V diesel makes a difference here(?) The lower torque advantage of gas engines at idle may make it a better fit for using the rudder while not moving; I don't know.

 

[RollerCoastr]

Individual experiences/setups may vary.

Very true. Some boats will walk, others don't. Torque, rudders, keels, wheels, prop pockets all play a roll in boat handling.

I can barely make mine walk, so I don't even bother trying. I've learned what my boat responds to and I adapt to it. She doesn't like to be argued with. :grin:

 

[JV II]

Everyone understands that when a single prop rotates, it pushes the boat forward and also walks the stern in the direction of the prop rotation? Imagine your prop is a tire and your boat is on pavement. When the tire turns the stern goes in the direction that the tire turns. That's what happens when you engage the transmission of a single propped boat. The stern walks in the direction of the prop rotation. If you use one lever the stern goes to port. If you use the other lever the stern goes to starboard. I wonder how strong that effect is on, say a 340SD. It is pretty strong an a diesel 36 DB.