Trawler vs Motor Yacht Running Gear

I have talked to some Sea Ray and Carver owners that love their boats because they can go slow for economy, but have the option of going fast if needed. Its an appealing argument.
But when i look at their type of boat out of the water, I see v hulls with small rudders and extremly exposed drive shafts and props. ( I guess so they can go fast) My first thought when i see this is whats going to happen with a hard grounding or hitting a submerged object at speed? Seems to me you could take out the whole damn thing with bent shafts, props and rudders. In contrast most trawlers seem to have a keel for directional stability and running gear protection.
This big boat business is all new to me, but I plan on getting one for serious cruising when i retire in a couple of years. I dont want to make a mistake.

Am I exaggerating the problem? Can you run a boat like that at 8 knots, or will it be unable to hold a heading?

Thanks for any comments.

Uh oh. Deadhead ahead, in the middle of the channel for the Antioch (CA) Bridge:



I place high priority on propeller/shaft/rudder protection (along with 360-degree decks/visibility and strong/high railings.)

I had a single engine Marine trader that I run aground multiple times ,never hurt a prop or running gear . I now have a twin engine boat ,I ran aground one time in the Bahamas and had to buy 2 new props I miss my little single engine boat . the ironic part is I spend most of my time in the new boat running the same speed I did in the.single engine boat

Pluto

A twin engine trawler style boat generally leaves the running gear exposed, except for the limited protection the keel provides.

A single engine boat, as you noted offers significant protection to the running gear.

This concept has been, and will continue to be, the root cause of many passionate discussions here on TF, on the docks, and amongst boating enthusiasts for as long as we have boats with props.

The Grand Banks hull is nice in that in the twin engine models if the boat is grounded and the tide goes out, the running gear will not be damaged. This is because the shafts, struts, props, and rudders are located pretty close in to the fairly deep keel. (photo) So as the tide goes out and the boat goes over it will end up resting on the keel and the chine with the downside prop, rudder, and struts totally "protected" inside the resulting triangle of open space.

In the almost fifteen years that we've been doing this kind of boating we know or know of more owners of single engine boats (including sailboats) who have damaged their prop or rudder by hitting something or getting something wound up in the prop or shaft than we do twin engine owners who've had the same problems. I don't know if this is because twin drivers tend to be more vigilant about what's in the water ahead of them knowing their running gear is more exposed, where the single engine drivers blissfully cruise along assuming their prop, shaft, and rudder is suitably protected by the keel. In any event, twins or singles, it seems to make no real difference in the kinds of boats here that incur damage from debris, lines, nets, or a grounding.

We have a twin and so pay pretty close attention to what's in front of us. In situations where our course takes us close to or through fields of commercial crab pot floats both of us will be at the helm station looking ahead to pick a safe course through the obstacles. Same thing if the light is such that it makes stuff on the water hard to see. We'll both scan ahead of us to make sure we don't run over anything. If the water is calm most of the commercial crab pot floats show up quite well on radar, too, as they usually incorporate a large metal fender washer in their lashup.

Pluto said:

But when i look at their type of boat out of the water, I see v hulls with small rudders and extremly exposed drive shafts and props. ( I guess so they can go fast) My first thought when i see this is whats going to happen with a hard grounding or hitting a submerged object at speed? Seems to me you could take out the whole damn thing with bent shafts, props and rudders.

Thanks for any comments.

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You pretty much nailed it though no hull design is going to survive hitting the submerged object in Marks post.

If you want to go fast you're going to have to give up the protection a large keel and hull design provides or be happy at sailboat speeds.

I am much more careful about watching the depth in my current boat than when I had a sailboat. But I also can make it across the Gulfstream to the Bahamas in 4 hours or across the FL straits to Key West in half a day, not possible at Trawler speeds.

In the many boat yards I've been around I haven't see a slew of Carvers, Sea Rays, or Bayliners with bent shafts and twisted rudders, but it does happen.

The DeFever way! It certainly isn't as protected as the singles on my former boats, but that stuff is pretty damned robust
those are 24" wheels. The rudders are on the order of 30+" tall. The keel is 10" or so thick.

Mark,

Being out of Antioch and often passing the 160 bridge, I do not ever recall having seen this particular landmark.
Any chance you might have the GPS coordinates for it?

Thanks.

Jim, it was immediately west of the Antioch Bridge, in the main channel on April 25. It wasn't there/visible when we returned several days later. Presumably, it's slowly working its way westward.

Not only is the running gear better protected but the singles prop can be far larger in diameter and spun slower.

This reduces noise aboard and makes better prop efficiency.

Go fast is one style of boating , but running the go fast at displacement speeds requires many compromises.

Poorer efficiency with perhaps iffy steering and a poorer ride .

But it can be done.

Max prop size is not a function of single vs twin. It comes down to shaft angle ie. clearance from hull and/or skeg. We have the clearance for 36+" wheels yet twins.

Daddyo, FF,
Unless you have a totally flat bottom (rare in a trawler) the twins will have significantly greater room for a larger dia prop w the same draft.

But re FFs comment some singles are built so deep that larger props can be used. But not on most all trawlers. Fishing boats yes.

On some deeper craft the optimum size prop is considerably smaller than the space available. If you have a large dia prop w lots of blade area and a very low pitch reducing the dia and increasing the pitch can increase efficiency. Over powered boats run out of prop space quickly though.

motion30 said:

I had a single engine Marine trader that I run aground multiple times ,never hurt a prop or running gear . I now have a twin engine boat ,I ran aground one time in the Bahamas and had to buy 2 new props I miss my little single engine boat . the ironic part is I spend most of my time in the new boat running the same speed I did in the.single engine boat

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Usually when running aground in the Bahamas it is on a coral head. They can also cause hull damage. They will beat a prop until it's almost unrecognizable.

Some motor yachts have prop pockets and a smaller keel to at least get the keel a hair below the lowermost edge of the props to afford at least some protection to running gear.

Pluto:


So far lots of discussion on singles vs. twins - protected props, etc.

Questions:

1. How do you intend to use the boat? Coastal? Ocean voyages? Weekends? Live aboard?

2. Size you're looking for and budget?

3. If you're NOT ocean voyaging , is speed when you want it important? There's no voyager I know of that has the option of planing-type speeds.

No sense in making any suggestions till one knows your answers.

My father-in-law had a twin screw boat for years, said it gave him the protection against breakdown he needed. Bad load of fuel, I towed him in. One engine breakdown, he could only go in circles on the other engine, towed him in.

You know why they round over the aft top edge of rudders... So they won't pierce the hull when you bend over the shaft in a good hard grounding.

Brooksie said:

. One engine breakdown, he could only go in circles on the other engine, towed him in.

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Did the boat not have a wheel, or did he panic and forget to use it?

Woodsong said:

Some motor yachts have prop pockets and a smaller keel to at least get the keel a hair below the lowermost edge of the props to afford at least some protection to running gear.

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I know of a twin engine trojan that went hard a ground at.speed in the process driving the.struts up through the bottom of the boat sinking boat on the sandbar

Moonstruck said:

Did the boat not have a wheel, or did he panic and forget to use it?

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No panic, it would only go in circles ChrisCraft 30something express.

I have lost engines on twin engine boats, and always gotten in. In fact, backed into the slip. I lost steering on my single engine Blackfin. It was 12 miles out. Rigged an oar up to the swim platform made it in 6 miles before breaking the oar. Then it would just go in circles from the torque steer of the big Cat diesel. Had to be towed in. It was a bad day.

Aground in the Bahamas, but definitely not a bad day.

Moonstruck said:

I have lost engines on twin engine boats, and always gotten in. In fact, backed into the slip. I lost steering on my single engine Blackfin. It was 12 miles out. Rigged an oar up to the swim platform made it in 6 miles before breaking the oar. Then it would just go in circles from the torque steer of the big Cat diesel. Had to be towed in. It was a bad day.

Aground in the Bahamas, but definitely not a bad day.

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Did you make the crossing in the inflatable??

beachbum29 said:

Did you make the crossing in the inflatable??

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Good shot. No. Moonstruck was anchored around the corner. It was a soft grounding on the beach. After we get there, I put more miles on the inflatable that Moonstruck. It's our "car".

Brooksie said:

One engine breakdown, he could only go in circles on the other engine, towed him in.

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Interesting. All the twin engine boats I've ever seen in the big Seaview yard in our marina, including ours, have rudders. But I suppose if your dad's boat didn't have rudders losing an engine could be a problem.

We've brought our boat back on one a few times, all due to raw water cooling problems, not engine problems, except the one time I let an engine get a slug of air during a fuel transfer-- my fault, not the system's fault. One of the runs was six hours on one engine. I do not recall going in circles during that run but it was a number of years ago so I may have forgotten that we did.

And having twins does not automatically mean running gear damage in a grounding. As I mentioned earlier, a Grand Banks with its keel that extends considerably below the props and rudder, will lie over on its side with the downside running gear totally protected in the open space between the chine and the bottom of the keel, which is what the boat sits on when the tide goes out.

Moonstruck said:

Good shot. No. Moonstruck was anchored around the corner. It was a soft grounding on the beach. After we get there, I put more miles on the inflatable that Moonstruck. It's our "car".

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I'm just jealous. We've never been. Hopefully this fall, after we get the new boat sorted out, then we will go over.

markpierce said:

Jim, it was immediately west of the Antioch Bridge, in the main channel on April 25. It wasn't there/visible when we returned several days later. Presumably, it's slowly working its way westward.

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Hopefully it worked it's way into the junkpile in Mayberry Slough. It still amazes me that Sac County has never done anything about that eyesore.

We have lots of debris in the river after really high tides and/or heavy rain. Several of our friends with Searay's have had to replace props, rudders and shafts after hitting partially submerged logs. The boats that really scare me are the ones with the pod drives. There is one Tiara in our marina with them and I'd hate to think of the damage if he were to hit something big at speed.

beachbum29 said:

I'm just jealous. We've never been. Hopefully this fall, after we get the new boat sorted out, then we will go over.

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Great! Hope you first trip is a good one. I recommend the Abaco area for a first trip or any other trip for that matter to the Bahamas. Depending on speed you will have one or two days to Ft. Pierce. When the weather is right, hang a left and head over to the Little Bahama Bank. Enjoy.

compromise

Here is a different look at recessed props from my 38 semi displacement hull. Note that the keel is safely quite a bit below the twin props. Considering that everything in boat design involves compromise, I do think, because I regularly run in low water and regularly scrape bottom, this particular design has been good for me. Knock on wood but no prop or strut or shaft damage in two years. A little glass thickening on the keel is about it. The compromise I face with this configuration is poorer steering in following seas and a bit more roll than I would like in rough water. As well my max WOT is about 21 mph.
Being able to operate like an economical diesel trawler is nice most of the time but burning money once in a while to make waves is nice too. In western Lake Erie a full trawler (or a proper one as some might suggest) with a deeper keel would really restrict my travel.

The common denonator here from reading the posts and from my own experience is not prop protection, its boat speed.

Take my boat for example. It has twins and a full keel.

At a 15 knot fast cruise things happen quickly. Logs are much harder to avoid. The bow is higher which means if we do hit a log it has a tendancy to be pushed under the boat, into the running gear. The higher bow also reduces visibility

Now take the same boat at 8 knots. Going slower provides manuvering time. The bow is flat in the water which helps push logs out of the way if you do hit one. Visibility is at its maximum which provides for increased hazard recognition.

Now take my old boat, and what actually happened to me.

We had a 34' Bayliner 3488 Avanti. This was a full planing hull boat, with a flying bridge, a lower helm and with 630 horsepower a 26 knot cruise speed.

I was offshore in Alaska and hit a log going full speed. Both rudders bent back, and the rudder shafts started some serious flooding of the engine compartment. With our owner installed oversized bilge pumps we were able to make it back to port where we had called ahead and had the travellift standing by.

The boat sustained over $40K in damage including one of the cummins diesel engines which had ingested seawater into the air intake system because of the seawater being sprayed onto the air cleaner for several hours. Both rudder assemblies, both props, struts, damage to the hull. It was an extensive list.

We impacted at 26 knots. If we had been running at 8 knots, same boat I'd dare say the damage would have been much less, and possibly eliminated.