Planing with a Semi-Displacement Hull

[Alaska Californian 37]

Does anyone have resources or links regarding making a semi-displacement hull plane? ie. power/weight ratios etc.

Someone told me they thought my 38' Californian LRC would plane with an engine swap and now I'm curious.

I'd especially like to hear from any Californian owners that have researched already done this.

 

[Nomad Willy]

I suspect all you need is more power. Probably lot’s of it.

The Californians I’ve seen (out of the water) have a straight run in the aft part of the hull. Basically a planing hull. If the bottom is’nt hooked or hogged 30 knots or more should happen w enough power. The lighter the engine the better .. for speed.

Power to weight ratio should be the same. But I don’t remember if the Californian has a significant keel. If so calculate the surface area of the keel and ad it to the bottom of the hull for your calculations.

Wanna share your reasons for the need for speed? You probably should get a Uniflite or Tollycraft instead.

 

[OldDan1943]

Yes, if you put 2 Allison airplane engines (1000 horse power each) in the boat, it will plane but at what cost. Think of the size of the fuel tanks you will need. LOL
I suggest/encourage you keep the current engine(s) and be happy.
Take EVERYTHING off the boat go WOT and see that you can plane. Then put all the stuff back on the boat, go 1,000RPM and be thankful with the fuel economy.
If your friend recommends a engine(s) swapping, let him pay for it.
Why it is so important to plane your boat?
Trust me, it's not worth the expense and added fuel and repair. Enjoy what you have.

 

[markpierce]

If you want your boat to plane, it is probably less expensive to sell your current boat for one that goes as fast as wanted.

 

[C lectric]

Which engines do you have right now?
HP rating and model?
What kind of speed can you make right now at wide open throttle? Don't need to do that for more than enough time to get a boat speed reading. It need only be approximate.
How much faster do you want to go?


As a very rough starting point for costs of any shop done swap like this is going to start at $60K-$80K. Just what I have seen from people who have done or contemplated swaps for similar reasons. Some of them did the swap, some balked.

In addition to the engine you will likely need new shafts, new struts and stuffing boxes to accommodate a larger shaft, new gearboxes to handle the power, new engine mounts and the locations and support bracketry will be different.

While in there there is very likely other work that will need to be done to do a good, successful job.

You will likely lose the boat use for at least 3 - 4 months and then comes debug time.

 

[Alaska Californian 37]

Just curious is all. I'm perfectly content operating at displacement speed, but the idea of my boat on step makes the kid in me excited. lol

 

[Alaska Californian 37]

Again, not really asking for what others think I should do... asking for links/experience with people who have actually done it. If I cared about fuel economy or swap issues, the question wouldn't have been asked.

 

[Alaska Californian 37]

Perkins 6.354 nat w/ Velvet Drives. 14 kts. Not worried about cost or amount of work required rn, just looking into what it would take. Have another friend that put twin jets on his commercial fishing boat and does 42 kts fully loaded. Again, just curious and want to research data myself and hear from others about their experience.

 

[rsn48]

My boat when purchased could go 11 - 12 knots or so on plane but not by much. The short story was I didn't know what I was doing put in a new Merc gasser thinking I might get to 18 knots but instead ended up at 30 knots.

I like the speed, my most efficient cruising speed on plane is 22 knots. Ironically this has resulted in reducing the size of my cruising area. By this I mean, something that might be a 4 to 6 hour cruise is now reduce to 1 1/2 to 2 1/2 hour cruising. Places that seemed far away in terms of time are now much closer. I find I like this and dislike it. It was kind of neat to plan the "big" journey. Now I can leave at noon and be at some great location in 2 hours.

 

[rslifkin]

Perkins 6.354 nat w/ Velvet Drives. 14 kts. Not worried about cost or amount of work required rn, just looking into what it would take. Have another friend that put twin jets on his commercial fishing boat and does 42 kts fully loaded. Again, just curious and want to research data myself and hear from others about their experience.

I'd be curious to see what the wake looks like at 14 kts. If it'll do 14 kts with that power, yeah, it'll probably plane with more.



Semi displacement hulls vary. Some will exceed hull speed by a bit, but it's hard to make them go more than a few kts over. Others will sorta-kinda plane given enough power, but burn a ton of fuel at that speed and throw a massive wake. And others are really a halfway decent planing hull that just wasn't given enough power to plane.

 

[Nomad Willy]

Numerous trawlers have planing hulls that are considered to be SD because they won’t go over 10 knots.

A SD hull has a different shape than a planing hull or a FD hull. Both can have rocker .. a part of the hull that is convex as viewed from the side. But it can be convex only in the middle or at one end or the other. A flat bottomed dory-like boat may have rocker that is mostly or all in the aft end of the hull. If you try to run such a boat fast it will run very bow high. If the rocker is considerable it will pull/suck the stern down and eventually render the boat uncontrollable as one goes faster.

But if the rocker is only slight or moderate and roughly centered in the hull speed well above HS (hull speed) can be had. Like an 8 knot HS boat running at 12-15 knots. Can’t call it a planing hull as it won’t achieve planing speeds like 20-25 knots and dosn’t have a planing hull shape. But it may achieve planing speeds at the very bottom of the planing range as in 12-15 knots.

But a tricky hull is the SD hull that has rocker fwd of the center of the hull. Such a hull is unusual. I can only think of flat bottomed boats that have this feature. The trick is that when given enough power they can or may run bow high enough to get the rockered part of the hull out of the water and the stern/transom below the WL as typical of planing hulls. But this hull has a straight run aft from the hull center. So all the boat below the WL is just as a planing hull would be. Wm. Atkins designed such a boat and I think they should be considered as SP/SD hulls. I’m quite sure they (several perhaps) were designed as SP/SD hulls, capable of 12-15 knots w an 8 knot HS. But under certain circumstances like trim/ballast that would be unusual .. higher planing speeds could be achieved .. like 20 knots. Most would, however consider this a SD hull.

So to achieve normal everyday planing speeds to run at a normal planing hull would be required. That would be a hull that has a straight run aft from the center of the hull or a bit fwd. the planing hull will have small rudders, almost no keel and most importantly low overall weight.

Relative to this thread the Californian boat probably is somewhat overweight to be a planing hull. As I’ve said before I’m not sure about their keel or if they have one.
But I’m fairly sure they have the straight run aft that is required and if so the Californian should be capable of full planing speeds. The extra weight that’s probably there, in lower levels than most planing boats, could be overcome w huge amounts of power as indicated my numerous comments above.

 

[DDW]

Just curious is all. I'm perfectly content operating at displacement speed, but the idea of my boat on step makes the kid in me excited. lol

When you see the fuel consumption your fuel dock will get excited. On my boat, 7 knots is 1.7 G/hour, 17 knots is 20 G/hour