Planing vs semi displacement boats

[colingr]

Just looking at the Jersey 30 and thinking it looks like a nice boat for when I want to stop haring around on the plane scaring raggies.

A question, I can see that it will be more stable than the Monterey at displacement speeds due to the hull shape and probably a lot cheaper to run but what about when it is in semi mode as it were. Do they start to guzzle fuel, how do they handle compared to being up on the plane?

If I move up I wouldn't want to be limited to displacement speeds, might as well cross to the dark side for that, or should I just stick to a planing boat.

Views / opinions?

 

[Canopy Locked]

No doubt there will be other with vastly more experience. On my Mitchell 31 (semi d with bilge keels) the 320 hp engine used around 31 Ltr/Hr at a sensible cruise speed - around 14 kts. Push this up to 19 kts and the fuel consumption would easily be double.

In my experience with planning boats (sub 24ft) they have pretty much 2 speeds.. displacement and planning... it's difficult to give precise comparisons.

I loved my Mitchell for its comfortable ride..... I dislike the ride in my current angling boat in anything but quite calm water, but it's quick..!!

As they say... Pay yer money..... take yer pick!

 

[Bertramdriver]

My Bertram SD Hull had two speeds. She's really happy at 8/9 knots and 18 knots. The big advantage of a SD over a pure planing hull is that when the waters are fairly calm you can cruise economically at 8/9 knots but if the slop picks up and the ride becomes uncomfortable, piling on another 3 or 4 knots will lift the bow and provide a more comfortable ride as the bow wave "suppresses the waves". I've never managed to play that trick with a planing hull. Also being able to crank up to 20 knots when bad weather is building can get you to safety before the heavens open.
Some will say that a SD hull neither planes well nor drives well at displacement speeds, however that is like comparing a BMW 520 with a Range Rover. Which is better? Depends what kind of boating you do, but for me I have an SD and a Range Rover. ABTW what kind of hulls do the pilot boats, and RNLI use? SD.

 

[colingr]

ABTW what kind of hulls do the pilot boats, and RNLI use? SD

That's a very good point, well made. Also agree with your point about planing boats when the going gets rough. Slamming becomes the order of the day.

 

[piratos]

Just looking at the Jersey 30 and thinking it looks like a nice boat for when I want to stop haring around on the plane scaring raggies.

A question, I can see that it will be more stable than the Monterey at displacement speeds due to the hull shape and probably a lot cheaper to run but what about when it is in semi mode as it were. Do they start to guzzle fuel, how do they handle compared to being up on the plane?

If I move up I wouldn't want to be limited to displacement speeds, might as well cross to the dark side for that, or should I just stick to a planing boat.

Views / opinions?

Planing vs SD always gives a discussion, whther you prefer Full planing or Semi displacement boats is very subjective.
The Displacement speed will be just 7 knots full planing 20 knots plus

My view is clearly that if you regularly wants speed in excess of 20 knots you should go for full planing hull.
The SD will run fine between 7 and 20 knots. It might even be able to reach speeds in excess of 20 knots, but thats when it becomes expensive to run a SD.

I dont know the Jersey 30, but I would not go so far as to say the SD is more "seaworthy" than the Full planing boat. Your will always find good reasons for either view.
You will have to compare the candidates every time.

If the Jersey 30 otherwise suit you well, then why not use the speed potention it has at best ???

 

[Chamaerops]

I was experimenting with different speeds at the weekend with the SD Merry Fisher 645 with Yamaha 115 outboard.
At displacement speeds of 4-5 knots economy is about 2 miles/Lt., increasing to between 6-8 knots it is about 1 mile/Lt. And planing at about 25 knots this came down only fractionally to 0.8 miles/Lt.

 

[Bertramdriver]

I was experimenting with different speeds at the weekend with the SD Merry Fisher 645 with Yamaha 115 outboard.
At displacement speeds of 4-5 knots economy is about 2 miles/Lt., increasing to between 6-8 knots it is about 1 mile/Lt. And planing at about 25 knots this came down only fractionally to 0.8 miles/Lt.

Envy......if only. 8 knots, 4 litres per mile. 20 knots, 16 litres per mile. 2 x 435 hp Detroit Diesels. 20 Tonnes all up !!!

 

[RogerRat]

A question, I can see that it will be more stable than the Monterey at displacement speeds due to the hull shape and probably a lot cheaper to run but what about when it is in semi mode as it were.

Also agree with your point about planing boats when the going gets rough. Slamming becomes the order of the day.


Views / opinions?

SD versus planing is right up there with shafts and outdrives. :sleeping:

But you have to compare like with like. Your Monterey is a great little boat but is an American lake boat like the Bayliner, as the chop picks up so will the slamming. Any wind over tide on the bow above 20 knots will start you bouncing, trimming and/or slamming. If you get a deeper V on a Fairline type boat, not necessarily much larger, a Targa 34 is a good example, you will cut the water better and get a far smoother ride. I don't want to push Fairline down your throat as that's not my intention. My Targa 40 will do 35+ knots into a force 5-6 in the Solent but... above 30 knots, it's horrible, that's why I didn't open her right up!

The point is, there a planing boats and there planing boats!

The true SD boats as chosen by the Coastguard and lifeboats look great when they're cutting through with a bow wave peeling over past the gunwhales, but remember, they're not paying for the fuel. We are!

Smaller SD boats, below 35 foot even at SD speeds are very prone to roll in a following sea, where as your Monty is great on that point of sail. If ever you have guests that are prone to sea sickness, this is where they'll start to feel ill. Apart from the motion, the wind will be aft and exhaust smells will catch you up because you will be going slower like an old charter fishing boat.

Two speeds, yes, on a true planing boat, (the ones where you actually get over the hump of your bow wave) there are only two speeds waterline length displacement and properly on the plane throttled back a bit where she fells comfotable on the day. Wind, waves, tide, cr4p on the bottom, fuel load, crew and trimming will make this slightly different almost every time, only you will feel it as no one knows your boat like you do. Remember, if you're not planing, just look at your wash and you'll see how much fuel you're wasting.

Larger, shaft driven boats 40 foot plus don't really plane as above, they just ride up onto a smaller wetted area further back. Displacement speed on water line length again most economical. Somewhere throttled back from max is most economical, but again the best place to sit is where most comfortable on the day, this could be somewhere between 15 & 25knots depending on the skipper, the need and sea conditions. At least with these boats you have the option to travel quicker when needed but they are nice also when running slowly.

For private boating, the so called SD, gentlemans' twin screw motor yacht below 35ft is even more of a compromise imho, for old school yachties' that can't really make the break and cross over, they get neither of the best of both worlds and pay out on loads of fuel not going more that 15 knots.

Don't get me wrong, there are some beautiful large ones out there, like Flemming, Zeelander, various trawlers, grand banks and Sea ranger for example, it's just that they would be a far cry from a light weight planer like the Monterey.:nonchalance:

There you go tuppenceworth::encouragement:

RR

 

[Greg2]

What Roger said!

We have had all types of boat including a very shallow V planing hull, a deeper V planing hull on a Targa 35, a SD Broom and our current planing hulled Broom (41 feet in length). By far the best all round boat is the current one as it displays the characteristics described by Roger. It doesn't get over the hump like the Targa but lifts as speed increases. We have cruised at all speeds from 6 to the usual 18 knot cruising speed and it probably has the benefits that you are seeking in a SD hull without the drawbacks. The Targa hull certainly didn't do that but it wasn't a bad boat....probably one of the better in its class actually.

I think that make and model has a huge influence so choosing carefully can be important. For example the Broom Ocean 38 is a SD hull but from what I hear proved to be a very good sea boat (oceanfroggie has one so can probably offer a better opinion) so not a precise science.

 

[RogerRat]

What Roger said!


I think that make and model has a huge influence so choosing carefully can be important. For example the Broom Ocean 38 is a SD hull but from what I hear proved to be a very good sea boat (oceanfroggie has one so can probably offer a better opinion) so not a precise science.

Aahh, chucks. :applause:

I know what you mean about the Broom and her Atlantic cousin, although not a personal favourite, it does offer so much in the world of compromise:

Not bad looking, high quality build and solid.

Large saloon as no space used by a lower helm. ( Not every one likes this tho)

Good sea keeping reports as Greg said, 'Ocean Froggie' has put up some great threads from long passages he has made in the past.

Genuine, variable speed boat and soft ride. Happy and more economical at lower speeds.

However, there is a Big Broom 50 in Lymington that has the largest engines they had ever installed: I think they were 800Hp if memory serves me. This was a quick boat and looking extremely comfy doing it.

I was catching him up pretty quickly one bright day on My Targa 40 when he was cruising at around 30 knots. I noticed him increase in speed to match me at about 33 knots, so I gave it a little extra, (as you do) not having that old 'pipe & slippers' Broom in front of me, I thought. As I started baring down again at about 100 yards range, he gave her some more. I was along side her at 38 knots, I had to hit 40knots, nearly WOT o) to leave him in the approach to Lymington.

I was that impressed that I had to go around to his berth for a chat, the owner was pretty proud of her and loved the 'Wolf in Sheeps clothing' analogy.

There are boats like the Targa 52 that Adrian B used to have, with D12 715s' on that would kick you in the back straight over 30 knots and would also do 38knots WOT. Boats of this size are very impressive when they pick up their heels. Only drawback, is that your wallet would begin to squeal under the cost of fuel burn!:ambivalence:

RR

 

[colingr]

Great replies thanks, much to think about. As I'm unlikely to go much above 30ft (well who knows) maybe sticking to a full planing hull like a Sealine / Fairline might be better. I've been out on an SD Ocqueteau (sp?) 25ish footer fishing and it does seem to roll around in the swell I must say. Must try to get out on a larger planing / SD boat sometime to compare.

For the moment I'm still enjoying the Monterey but thinking one day I might grow up

Unless of course the right boat comes along at the right price.

 

[boatmike]

The very first thing you need to decide on is what you want a boat for. Sounds simple but do you only go a short way offshore in mainly clement conditions? If so a full planing hull will get you to your fishing spot more quickly and consume less fuel and if you are careful to watch the weather will get you back quickly too if you are not too far offshore. The SD hull like my Aquastar 33 comes into its own in conditions where most lightweight planing hulls would be very uncomfortable on the plane and will roll like a pig at displacement speeds so much more suitable for extended offshore work but yes they are more expensive to run because they are not lightweights. As someone else said the RNLI don't have lightweight planing hulls for going offshore. They do have RIBS though for inshore rescue. Its all about doing the job. What job do you want done?

 

[colingr]

Who knows just idly dreaming at the moment

When the girls are aboard we want to go towing ringos and blatting about. The Monterey is perfect for that and even for longer trips like around the Island / Swanage or Poole is OK if the weather is clement.

When it's just me and the boss a quieter cruise to a nice anchorage for sitting in the sun and relaxing. I'd like to do more longer cruising so a bit slower but more range. It all depends on when the girls bow out of our boating life I suppose. I'm thinking of a diesel powered 30ish footer that can maintain 20 - 25 knots without breaking the bank (at least not more than necessary). Big enough to stay on for a few nights. The Monterey is a bit cosy for more than an overnighter.

I quite like Fairline / Sealine options I must admit if going the planing route or something like the Jersey 30 style for plodding / fishing. Sadly an SC35 is out of my range.

 

[piratos]

Who knows just idly dreaming at the moment

When the girls are aboard we want to go towing ringos and blatting about. The Monterey is perfect for that and even for longer trips like around the Island / Swanage or Poole is OK if the weather is clement.

When it's just me and the boss a quieter cruise to a nice anchorage for sitting in the sun and relaxing. I'd like to do more longer cruising so a bit slower but more range. It all depends on when the girls bow out of our boating life I suppose. I'm thinking of a diesel powered 30ish footer that can maintain 20 - 25 knots without breaking the bank (at least not more than necessary). Big enough to stay on for a few nights. The Monterey is a bit cosy for more than an overnighter.

I quite like Fairline / Sealine options I must admit if going the planing route or something like the Jersey 30 style for plodding / fishing. Sadly an SC35 is out of my range.

If you are looking at 30ish footer with speeds of 20-25 kinots forget about SD boats. To reach this speedlevel in a 30ft boat, you need full planing.
On the other side, if all you need this speed for is towing ringos....then it might be cheaper to buy something slower (SD) and a tender with a 10-15 hp outboard. It can be deflated and stowed away

 

[colingr]

If you are looking at 30ish footer with speeds of 20-25 kinots forget about SD boats. To reach this speedlevel in a 30ft boat, you need full planing.
On the other side, if all you need this speed for is towing ringos....then it might be cheaper to buy something slower (SD) and a tender with a 10-15 hp outboard. It can be deflated and stowed away

I think the need for ringoing is fast disappearing as the girls grow up. Will save a fortune in fuel if nothing else

Cruising at 25 is the most likely scenario for the future.

Anyone want to swap a cruiser for a cracking good sports cuddy? :encouragement:

 

[rustybarge]

If you are looking at 30ish footer with speeds of 20-25 kinots forget about SD boats. To reach this speedlevel in a 30ft boat, you need full planing.
On the other side, if all you need this speed for is towing ringos....then it might be cheaper to buy something slower (SD) and a tender with a 10-15 hp outboard. It can be deflated and stowed away

S/D hulls use a lot of fuel at 15kts because the hull is still in transition between displacement and getting onto the plane. The boat is pushing a wall of water in front of the bow, in exactly the same way as a planing boat at 15kts is trying to get over the same hump.....the merit of a S/D hull is its stability at that transition speed over the planning hull which is mushing along bow pitched high in the air.

Commercial operators have found a solution to this dilemma of wanting a dual purpose hull that is fast, stable at 15kts and easy to steer at displacement speeds without the dreaded deep vee side to side oscillation.

The botnia range of planing patrol boats can can stay on the plane at just 10 kts, top out in the high 30s, and steer straight at displ, speeds.

Good mid 1990s are roughly about 50k to 60k.........thay will take on all sea conditions, in fact a Botnia was the only boat that completed the round Britain race a few years ago, the conditions got so bad around lands end that all the ribs had to turn back but the Botnia just kept plowing on through storm no problems.....

 

[colingr]

There's a Botnia where we keep the Monterey. Described as the Land Rover of the Seas

Certainly looks the part I must say.

 

[boatmike]

I think you need to do some research about the performance of various boats. "Cruising at 25 knots" is not realistic for any small boat such as you invisage. My 33ft Aquastar (semi-displacement) can reach a MAXIMUM of 22knots using all of her 400HP. A realistic CRUISING speed for me is between 12 and 15 knots and even at that speed the fuel consumption averages out at at about 1.2 miles per gallon. At 25 knots it is less than a mile per gallon. A small lightweight 30 ft PLANING boat will consume much less fuel at these speeds but you certainly won't CRUISE at 25 knots and in anything over F4 you will find it mighty uncomfortable over 20 knots. You will possibly be able to belt at 20 knots or so in calm water for short passages but that is not what most of us would call "cruising"

 

[colingr]

I think you need to do some research about the performance of various boats.

I thought that's what I was doing here.

You will possibly be able to belt at 20 knots or so in calm water for short passages but that is not what most of us would call "cruising"

We hare around at 35 - 40 knots and cruise at 25. We potter at anything less than 20. (definitions are mine only e& oe, other definitions may exist and may, or not, be more widely adopted)

From the general description of SD boats and performance I'm coming to the conclusion that I'll still want a full planing hull.