High Thrust vs. Regular Motor

[Stan Snapple]

I’m about to purchase a Yamaha 60hp (4-stroke) for the Commuter 27 that I'm building.

Can anyone recommend whether to buy the High Thrust or regular model? From what I read, the High Thrust is designed for heavier boats. It has a bigger propeller and turns slower. The regular 60hp spins faster. Again, from what I’ve read, I think the Commuter27 is not so heavy that it needs the High Thrust. And for that reason, I’m inclined to go with the regular, faster motor. Any tips appreciated!

Boat specifications
Single-chine power cruiser
L0A 27'
LWL 26' 5"
Draft 10"
Displacement 4000 lbs

Recommended motor 50-70 HP4-Stroke
Cruising speed 12-25 knots

[Gordon Bartlett]

I suspect you'd be much better off with the high-thrust lower end. That's a huge planing boat to be pushed by a 60hp motor. Most 60hp outboards are probably found on 16 footers, or thereabouts. In fact, my own 16 foot fishing boat wears a 50. With a light load for fishing, it will get up to 32mph. During duck season, when loaded with two guys, a full load of decoys and other equipment, and pulling a small (150 lb.) layout boat, it barely gets into the low 20's. Mine does not have a high-thrust lower end, but it does have a low-pitched "power prop". Even loaded like that, my boat is less than half the weight of yours.

[Stan Snapple]

Hmm... Do I have to consider upping to the 70hp?

[BillP]

Have you asked Parker this question? He should have an idea. My thinking is it might run on top and the bow vee gently cleaving with the standard engine and prop dialed in.

[Thorne]

http://forum.woodenboat.com/showthre...regular-thrust

[Stan Snapple]

Hi Bill, I did ask Reuel. And you're correct about the hull form. Parker says the 60 regular thrust is fine and that even the 70 is not necessary. I'm asking here because I too thought 60 is pretty small for such a big boat.

[skaraborgcraft]

We used a high-thrust 50hp on a large RIB, which is quite light, but was often used to tow much larger and heavier boats, at low speed, so the torque and bite of a larger prop to get going and stopping was a worthwhile. You will find your top end reduced slightly, so much depends on how fast you want to go.

[Ian McColgin]

One of many things I admire Capt. Parker is his very specific design for a purpose, avoiding that nightmare of military development known as mission creep. His power boats in particular have a designed speed and horsepower range and do not accept overpowering.

[Stan Snapple]

One of many things I admire Capt. Parker is his very specific design for a purpose, avoiding that nightmare of military development known as mission creep. His power boats in particular have a designed speed and horsepower range and do not accept overpowering.

Indeed. I've been in touch with him. I'm now trying to decide between a 60hp or 70hp. Both Yamahas with regular thrust. The design calls for 50-75hp. I know both will be fine! But I guess the question is whether the extra $1000+ for the 70hp is worth it performance wise.

[phiil]

I use a 60 hp high thrust Honda on my Bluejacket 25.5. Seems to work just fine, and my displacement is probably a tad less than yours.

[Stan Snapple]

Yeah, the Commuter is estimated 4000 lbs displacement – about 1000 more. Would the 70 be too heavy, too fast for your boat?

[BillP]

10 hp more might get a little more load carrying ability with more fuel burn but I doubt you will see a huge difference. I had a 50 hp Yamaha 4 stroke standard and it burned about 4.5 gph at 5500 on a 2500 lb pontoon with 6 people and picnic stuff aboard...speed dropped from 19 mph empty to 14 mph loaded. The 60 & 70 are the same basic engine...cubes, weight etc. The 60 is rated at 5500 rpm and 70 at 5800 rpm. It never hurts to have more hp but unless you are the type that can freely throw a $100 bill into the toilet and flush it without flinching I'd go with the 60 for $1k less.

Just saw the gph was incorrect...should be 4.5. Eye surgery last week isn't helping my vision yet!

[Gib Etheridge]

See if you can borrow a 60 and see how it does.

[Stan Snapple]

Thanks everyone! Bill, your metaphor resonated. So I bought the 60hp and feel good about it!

10 hp more might get a little more load carrying ability with more fuel burn but I doubt you will see a huge difference. I had a 50 hp Yamaha 4 stroke standard and it burned about 4.5 gph at 5500 on a 2500 lb pontoon with 6 people and picnic stuff aboard...speed dropped from 19 mph empty to 14 mph loaded. The 60 & 70 are the same basic engine...cubes, weight etc. The 60 is rated at 5500 rpm and 70 at 5800 rpm. It never hurts to have more hp but unless you are the type that can freely throw a $100 bill into the toilet and flush it without flinching I'd go with the 60 for $1k less.

Just saw the gph was incorrect...should be 4.5. Eye surgery last week isn't helping my vision yet!