Moving to Full Displacement Hull

[Northend]

I hope to draw on your knowledge and experience.

I'm thinking about moving from my Ranger Tug 29 with semi-displacement hull, to a full displacement hull (Kadey Krogen), and have some concerns about the full displacement hull's handling characteristics in strong currents. Particularly, when entering and leaving rivers and traversing currents.

With full-displacement hull-speed of only 7-8 knots, how difficult is it to pilot with strong currents. I imagine one would simply enter these areas during slack tides.

Any thoughts would be helpful.

Thanks, Northend

 

[Portage_Bay]

Start with slack or near slack currents on your first attempts. Gradually ramp up to faster currents learning your boat's capabilities and developing your skills. 3 - 4 kts current for most FD boats is managable with a bit experience. Faster currents if you're willing to accept the risks. In my opinion heading down current is riskier than heading into the current. Down current you will be moving over the bottom towards any hazards at the speed of the current should you need to stop. This could require turing around or backing at high velocity to avoid the hazard if too close to steer around. Up current simply back off on the throttle to buy yourself more time and "room" to avoid the hazard.

When the current matches or exceeds your maximum speed you obviously cannot go up current. Down current you will be at the complete mercy of the current if anything goes wrong.

 

[DavidM]

There is a lot of misplaced fear of currents, at least on the east coast. I have navigated The Race, Hells Gate and Woods Hole to name a few, in displacement hull boats going 6-7 kts at full flood or ebb with no problems.

The only thing you really have to worry about in those conditions is loss of power where maybe having twins would help but the consequences are the same whether it is a full, semi or planning hull with only one engine.

And yes maybe the current can sometimes hit 6 kts in those passages, but in my experience, more like 3-4.

David

 

[rslifkin]

There is a lot of misplaced fear of currents, at least on the east coast. I have navigated The Race, Hells Gate and Woods Hole to name a few, in displacement hull boats going 6-7 kts at full flood or ebb with no problems.

The only thing you really have to worry about in those conditions is loss of power where maybe having twins would help but the consequences are the same whether it is a full, semi or planning hull with only one engine.

And yes maybe the current can sometimes hit 6 kts in those passages, but in my experience, more like 3-4.

David

Agreed, people like to make a really big deal of some areas that aren't so bad in reality. Just a little awareness and planning makes most of them no big deal. I've heard all of the stories of not going through Hell Gate against the tide because you'll get thrown all over the place, there are whirlpools, etc. Yet I've done it (albeit not quite at full flow) and the only thing we noticed was a drop in ground speed for a bit due to the opposing current.

 

[Flatswing]

Not really an issue in practical terms up or down stream, although, the slower the boat, often you will find your course wandering as the current switches from 1 side of the bow to the other.
Entering or exiting a cross current can be exciting especially with longer waterlines but is usually predictable.
At our home Harbour, the narrow fairway has steel driven to block the waves/current but usually 2-4knots tidal current perpendicular outside the fairway. As I enter, the bow loses current effect before the full keel stern, if I over correct before the stern clears the break wall, it can get exciting. Now, I’m used to it.
whirlpool currents can be unnerving initially because they often move the entire boat sideways, yet often mostly corrects back to original course.
A bit of practice & you will feel comfortable

 

[PM]

I own a semi displacement 36 foot Albin. I have docked in wind, in river current, swirling current in locks and just about every other condition.

I never had a problem that I could attribute to the hull design, and at docking speed I don't think S.d is any different from full D.

I did REALLY have a difficult time once. Coudnt figure out why the boat was not responding to the wheel. Very sluggish, Almost had a mind of its own. I would steer port it would veer starboard, etc.

Can anyone guess what my problem was? (Don't peek, the answer is below my signature.)

pete

Very shallow water!

 

[RT Firefly]

Greetings,
Mr. N. I agree with Mr. PB in that going WITH the current is riskier that against it.



Years of white water canoeing experience proves, to me at least, the ONLY way you have any control of your craft, going with the flow is either moving faster or slower than the current. MUCH safer, in a canoe at least, back paddling when running rapids.

 

[guy with a boat]

I hope to draw on your knowledge and experience.

I'm thinking about moving from my Ranger Tug 29 with semi-displacement hull, to a full displacement hull (Kadey Krogen), and have some concerns about the full displacement hull's handling characteristics in strong currents. Particularly, when entering and leaving rivers and traversing currents.

With full-displacement hull-speed of only 7-8 knots, how difficult is it to pilot with strong currents. I imagine one would simply enter these areas during slack tides.

Any thoughts would be helpful.

Thanks, Northend

There are lots of us cruising in (or working from) full displacement boats and navigating currents regularly. Local knowledge of the specific currents and conditions is important. East coast and west coast perspectives will be different because the common conditions are different.

As a general rule, currents in a wide and deep channel or other body of water will affect your speed over ground (SOG) but aren’t a safety issue. When possible, you plan for those for the sake of expediting your travel. Currents in narrow and shallower areas can be a different story and are important to know about. Charts and guidebooks, among other sources, will indicate where those areas are. The issue then becomes the turbulence in those areas and is definitely a safety issue. Pass through those areas at slack current and you won’t hardly know they are there. The current tables and information needed are readily available.

Overall, not an issue at all with displacement boats. You just have to be aware and plan for the areas that can be sketchy. You really shouldn’t be in a narrows at full rip regardless of what cruising boat you have.

 

[mvweebles]

Story time. When I owned my Willard 30 in San Francisco with top speed of around 6-1/2 kts, I took my then girlfriend (now wife) to the Delta. I hadn't spent much time on tides and currents, and this was back in the day where you carried small tide chart booklets.

We headed to Benecia on a late Friday afternoon - head of the Carquinez Straits on way to Sacramento. Not fully comprehending the significance of all the info in the Tide Booklet, I blithely trundled up the straits bucking a 3+ kt ebb tide current. It took forever to get to Benicia. So i spent out trip in the Delta reading up on tide/current offsets and figured out we needed to leave to head home around 5AM. All good.

Running a displacement boat is a mindset. It's not for everyone. If you're prone to be precise about timing, could be frustrating. Notice in the opening paragraph I said "around 6-1/2 kts" versus "6.5 kts." Subtle but important difference in implied precision. People pay a LOT of money in engines, maintenance, and fuel to have the ability to out-run weather, arrive before sunset or lunch, or catch a bridge opening. If thats important, then displacement speeds may drive you bonkers.

As Guy with a Boat says, a lot of people running displacement boats. Not the majority, but quite a few. Until WW2, diesels weren't big enough to plane a boat so running displacement speeds was the only option. People have managed just fine.

Peter