Semi-displacement v. Deep V (R-27)

C

chronicity

Active member
Joined
May 19, 2018
Messages
35
Fluid Motion Model
C-28
Non-Fluid Motion Model
Suzuki 300 OB
Vessel Name
Addison Skye
MMSI Number
368047670
I've read as much as I can find on this forum regarding "classic" versus "new" R-27, from which I see there are many advantages of the outboard and new hull. My question is, what is the advantage of a semi-displacement hull as opposed to the deep V?

There must be some reason that Ranger/Cutwater didn't use deep V to begin with?
 
Here are things I would be looking for with semi-displacement over planing, and why I started looking at trawler-type boats:

1. Less bow rise. The first mate hates that. We'd like to stay as horizontal as possible.

2. Less leaning when turning. Our current boat feels like you are falling over when you turn at speed.

3. Better turning/steering stability in rough water.

4. Less messing with trim tabs just to get going.

5. Smoother/more comfortable/more "secure" feeling in moderately rough water (2-4'). (We will be mostly on inland NW lakes, and we won't typically see the rough seas that many of you deal with).

From what I've read so far, if I were to keep the new R-27 at say 8-10 (knots or mph?) it would feel pretty much the same as the classic boat in any type of water, and you have the advantage of being able to go faster if needed.

Hoping I can get a chance to ride on one of these soon. I really have no idea how they feel. My experience is with a large/heavy (25'/5000 lbs) inboard wakeboard boat (very flat in turns and very little bow rise) and now a 25' pocket cruiser (which I really don't like--points to the sky when getting on plane and feels like you're on a skateboard when turning).
 
Having just moved from a R-25 to the R-27OB, I can give you some feedback specific to those two boats.

1. Bow rise - this isn't really an issue on the R27....Ranger worked some magic on this boat. The boat pops up on plane and has great visibility in every situation I've been in.

2. Leaning at speed - think this is just the nature of a deep V.

3. Better turning/steering in rough water - if it's really rough, you'll probably be going slow in either boat and with the directional thrust of the outboard, I feel you have much better steering control. The inboard needs water moving across the rudder to be effective.

4. Trim tabs to get up on plane - Even with full fuel/water (150 + 40 gallons) and all the "stuff" we've put on, I've never felt even remotely the need for trim tabs. The R27 pops up on plane really well. I do adjust the tabs for list correction more on the 27, but this has more to do with speed. The faster you go, the more impact the trim tab has and needs to be retracted a bit to keep level.

5. Smoother in rough water - if I were in 4' water, I wouldn't be on plane and comparing the 25/27, I think the 27 is just as stable. I've been in some pretty good chop in the 27 and just went up on plane and shot through it. Not something you can do in the inboards.

Some of the advantages you get with the semi-displacement is a protected prop, less swinging on the hook (according to others), diesel is safer (although it foams like crazy...much prefer to fill the 27 compared to the 25...and I can see the fuel tank). In theory, a semi-displacement should rock less as people move around the boat than a deep V, but I haven't noticed a big difference. I think beam and displacement play a bigger role. You also should be able to get better fuel economy at a higher slow cruise speed in the semi-displacement compared to the deep V.
 
Thanks, KF91! The optimal "no-plane" speed is something I've been interested in between the two. I'd like to spend some time at displacement speeds, and I've been curious about how the new R27 is in that regard, for speed, steering control, and bow rise. I'm assuming that at displacement speeds, you are at near level in both?
 
Just for personal information I’d be interested if someone could post an rpm/speed/fuel consumption curve or data table for a deep-v 27. I’m particularly interested in the speed range 8 to 18 mph. Maybe 100 rpm increments for motor speed.

Thanks
 
I haven't spent a lot of time of at the slow range, but I will say the boat tracks really well when off plane. I don't have exact numbers, but about 7-8 MPH is the limit for slow/efficient cruising. 9-10 MPH and you are getting about the same mileage as going 25 MPH I believe. In the mid teens, you are in that awkward state between slow cruise and being on plane. I would say anything from 14-18/19 MPH is not something you'll spend time running as the economy will not be great and the bow will be up.

I can get some better numbers, but it may be a bit. Maybe some of the other owners can chime in.
 
Thanks Brian and Nicole,

That's exactly what I expected, classic modified deep V. It's those numbers from 10 to 25 mph and the transition that I'm interested in. Just for smiles, the last real deep V we owned was a 23 foot Boston Whaler Conquest. Very happy at 8 mph and I could actually get it to stay on plane in calm water with the tabs fully deployed and the motor pulled right in at about 18.5 mph. Most happy at about 32 mph and topped out at 48. Totally different boat of course.

The reason I'm asking is purely for personal interest. I spent my career in drive systems for everything from overland conveyor belts, buses, trains, gas pipelines to marine drives. Again, a widespread of marine craft there. Everything from high speed (100 mph +) to tugs, ferries and some military "stuff". All have a way over going over the hump if they are going to plane and it's interesting to see how modern design changes have evolved.

Hopefully someone else has done the detail numbers. I think you would find them of interest as well.
 
Thanks so much Dan. Just what I was looking for. Impressive numbers for a boat of that weight.
 
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